diff --git a/meson.build b/meson.build
index fcc0d7c..9f22f23 100644
--- a/meson.build
+++ b/meson.build
@@ -348,6 +348,7 @@
 srcfiles_bmcweb = files(
   'redfish-core/src/error_messages.cpp',
   'redfish-core/src/registries.cpp',
+  'redfish-core/src/utils/time_utils.cpp',
   'redfish-core/src/utils/json_utils.cpp',
   'src/boost_asio_ssl.cpp',
   'src/boost_asio.cpp',
diff --git a/redfish-core/include/utils/extern/date.h b/redfish-core/include/utils/extern/date.h
new file mode 100644
index 0000000..209e267
--- /dev/null
+++ b/redfish-core/include/utils/extern/date.h
@@ -0,0 +1,8254 @@
+// NOLINTBEGIN
+// clang-format off
+
+/*
+ *  Originally sourced from
+ *  https://github.com/HowardHinnant/date/blob/master/include/date/date.h
+ */
+
+#ifndef DATE_H
+#define DATE_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016, 2017 Howard Hinnant
+// Copyright (c) 2016 Adrian Colomitchi
+// Copyright (c) 2017 Florian Dang
+// Copyright (c) 2017 Paul Thompson
+// Copyright (c) 2018, 2019 Tomasz Kamiński
+// Copyright (c) 2019 Jiangang Zhuang
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+#ifndef HAS_STRING_VIEW
+#  if __cplusplus >= 201703 || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
+#    define HAS_STRING_VIEW 1
+#  else
+#    define HAS_STRING_VIEW 0
+#  endif
+#endif  // HAS_STRING_VIEW
+
+#include <cassert>
+#include <algorithm>
+#include <cctype>
+#include <chrono>
+#include <climits>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <ctime>
+#include <ios>
+#include <istream>
+#include <iterator>
+#include <limits>
+#include <locale>
+#include <memory>
+#include <ostream>
+#include <ratio>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+#if HAS_STRING_VIEW
+# include <string_view>
+#endif
+#include <utility>
+#include <type_traits>
+
+
+#ifdef __GNUC__
+# pragma GCC diagnostic push
+# if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 7)
+#  pragma GCC diagnostic ignored "-Wpedantic"
+#  pragma GCC diagnostic ignored "-Wconversion"
+#  pragma GCC diagnostic ignored "-Wold-style-cast"
+# endif
+# if __GNUC__ < 5
+   // GCC 4.9 Bug 61489 Wrong warning with -Wmissing-field-initializers
+#  pragma GCC diagnostic ignored "-Wmissing-field-initializers"
+# endif
+#endif
+
+#ifdef __clang__
+#  pragma GCC diagnostic ignored "-Wunsafe-buffer-usage"
+#  pragma GCC diagnostic ignored "-Wzero-as-null-pointer-constant"
+#  pragma GCC diagnostic ignored "-Wold-style-cast"
+#endif
+
+#ifdef _MSC_VER
+#   pragma warning(push)
+// warning C4127: conditional expression is constant
+#   pragma warning(disable : 4127)
+#endif
+
+namespace date
+{
+
+//---------------+
+// Configuration |
+//---------------+
+
+#ifndef ONLY_C_LOCALE
+#  define ONLY_C_LOCALE 1
+#endif
+
+#if defined(_MSC_VER) && (!defined(__clang__) || (_MSC_VER < 1910))
+// MSVC
+#  ifndef _SILENCE_CXX17_UNCAUGHT_EXCEPTION_DEPRECATION_WARNING
+#    define _SILENCE_CXX17_UNCAUGHT_EXCEPTION_DEPRECATION_WARNING
+#  endif
+#  if _MSC_VER < 1910
+//   before VS2017
+#    define CONSTDATA const
+#    define CONSTCD11
+#    define CONSTCD14
+#    define NOEXCEPT _NOEXCEPT
+#  else
+//   VS2017 and later
+#    define CONSTDATA constexpr const
+#    define CONSTCD11 constexpr
+#    define CONSTCD14 constexpr
+#    define NOEXCEPT noexcept
+#  endif
+
+#elif defined(__SUNPRO_CC) && __SUNPRO_CC <= 0x5150
+// Oracle Developer Studio 12.6 and earlier
+#  define CONSTDATA constexpr const
+#  define CONSTCD11 constexpr
+#  define CONSTCD14
+#  define NOEXCEPT noexcept
+
+#elif __cplusplus >= 201402
+// C++14
+#  define CONSTDATA constexpr const
+#  define CONSTCD11 constexpr
+#  define CONSTCD14 constexpr
+#  define NOEXCEPT noexcept
+#else
+// C++11
+#  define CONSTDATA constexpr const
+#  define CONSTCD11 constexpr
+#  define CONSTCD14
+#  define NOEXCEPT noexcept
+#endif
+
+#ifndef HAS_UNCAUGHT_EXCEPTIONS
+#  if __cplusplus >= 201703 || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
+#    define HAS_UNCAUGHT_EXCEPTIONS 1
+#  else
+#    define HAS_UNCAUGHT_EXCEPTIONS 0
+#  endif
+#endif  // HAS_UNCAUGHT_EXCEPTIONS
+
+#ifndef HAS_VOID_T
+#  if __cplusplus >= 201703 || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
+#    define HAS_VOID_T 1
+#  else
+#    define HAS_VOID_T 0
+#  endif
+#endif  // HAS_VOID_T
+
+// Protect from Oracle sun macro
+#ifdef sun
+#  undef sun
+#endif
+
+// Work around for a NVCC compiler bug which causes it to fail
+// to compile std::ratio_{multiply,divide} when used directly
+// in the std::chrono::duration template instantiations below
+namespace detail {
+template <typename R1, typename R2>
+using ratio_multiply = decltype(std::ratio_multiply<R1, R2>{});
+
+template <typename R1, typename R2>
+using ratio_divide = decltype(std::ratio_divide<R1, R2>{});
+}  // namespace detail
+
+//-----------+
+// Interface |
+//-----------+
+
+// durations
+
+using days = std::chrono::duration
+    <int, detail::ratio_multiply<std::ratio<24>, std::chrono::hours::period>>;
+
+using weeks = std::chrono::duration
+    <int, detail::ratio_multiply<std::ratio<7>, days::period>>;
+
+using years = std::chrono::duration
+    <int, detail::ratio_multiply<std::ratio<146097, 400>, days::period>>;
+
+using months = std::chrono::duration
+    <int, detail::ratio_divide<years::period, std::ratio<12>>>;
+
+// time_point
+
+template <class Duration>
+    using sys_time = std::chrono::time_point<std::chrono::system_clock, Duration>;
+
+using sys_days    = sys_time<days>;
+using sys_seconds = sys_time<std::chrono::seconds>;
+
+struct local_t {};
+
+template <class Duration>
+    using local_time = std::chrono::time_point<local_t, Duration>;
+
+using local_seconds = local_time<std::chrono::seconds>;
+using local_days    = local_time<days>;
+
+// types
+
+struct last_spec
+{
+    explicit last_spec() = default;
+};
+
+class day;
+class month;
+class year;
+
+class weekday;
+class weekday_indexed;
+class weekday_last;
+
+class month_day;
+class month_day_last;
+class month_weekday;
+class month_weekday_last;
+
+class year_month;
+
+class year_month_day;
+class year_month_day_last;
+class year_month_weekday;
+class year_month_weekday_last;
+
+// date composition operators
+
+CONSTCD11 year_month operator/(const year& y, const month& m) NOEXCEPT;
+CONSTCD11 year_month operator/(const year& y, int          m) NOEXCEPT;
+
+CONSTCD11 month_day operator/(const day& d, const month& m) NOEXCEPT;
+CONSTCD11 month_day operator/(const day& d, int          m) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, const day& d) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, int        d) NOEXCEPT;
+CONSTCD11 month_day operator/(int          m, const day& d) NOEXCEPT;
+
+CONSTCD11 month_day_last operator/(const month& m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(int          m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, const month& m) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(int          m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday_last operator/(const month& m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(int          m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, int          m) NOEXCEPT;
+
+CONSTCD11 year_month_day operator/(const year_month& ym, const day& d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year_month& ym, int        d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year& y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(int         y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, const year& y) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, int         y) NOEXCEPT;
+
+CONSTCD11
+    year_month_day_last operator/(const year_month& ym,   last_spec) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const year& y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(int         y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, const year& y) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, int         y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year&        y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(int                y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, const year&          y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, int                  y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(int         y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int         y) NOEXCEPT;
+
+// Detailed interface
+
+// day
+
+class day
+{
+    unsigned char d_;
+
+public:
+    day() = default;
+    explicit CONSTCD11 day(unsigned d) NOEXCEPT;
+
+    CONSTCD14 day& operator++()    NOEXCEPT;
+    CONSTCD14 day  operator++(int) NOEXCEPT;
+    CONSTCD14 day& operator--()    NOEXCEPT;
+    CONSTCD14 day  operator--(int) NOEXCEPT;
+
+    CONSTCD14 day& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 day& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const day& x, const day& y) NOEXCEPT;
+
+CONSTCD11 day  operator+(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 day  operator+(const days& x, const day&  y) NOEXCEPT;
+CONSTCD11 day  operator-(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 days operator-(const day&  x, const day&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d);
+
+// month
+
+class month
+{
+    unsigned char m_;
+
+public:
+    month() = default;
+    explicit CONSTCD11 month(unsigned m) NOEXCEPT;
+
+    CONSTCD14 month& operator++()    NOEXCEPT;
+    CONSTCD14 month  operator++(int) NOEXCEPT;
+    CONSTCD14 month& operator--()    NOEXCEPT;
+    CONSTCD14 month  operator--(int) NOEXCEPT;
+
+    CONSTCD14 month& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 month& operator-=(const months& m) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month& x, const month& y) NOEXCEPT;
+
+CONSTCD14 month  operator+(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 month  operator+(const months& x,  const month& y) NOEXCEPT;
+CONSTCD14 month  operator-(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 months operator-(const month&  x,  const month& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m);
+
+// year
+
+class year
+{
+    short y_;
+
+public:
+    year() = default;
+    explicit CONSTCD11 year(int y) NOEXCEPT;
+
+    CONSTCD14 year& operator++()    NOEXCEPT;
+    CONSTCD14 year  operator++(int) NOEXCEPT;
+    CONSTCD14 year& operator--()    NOEXCEPT;
+    CONSTCD14 year  operator--(int) NOEXCEPT;
+
+    CONSTCD14 year& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 year operator-() const NOEXCEPT;
+    CONSTCD11 year operator+() const NOEXCEPT;
+
+    CONSTCD11 bool is_leap() const NOEXCEPT;
+
+    CONSTCD11 explicit operator int() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    static CONSTCD11 year min() NOEXCEPT { return year{-32767}; }
+    static CONSTCD11 year max() NOEXCEPT { return year{32767}; }
+};
+
+CONSTCD11 bool operator==(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year& x, const year& y) NOEXCEPT;
+
+CONSTCD11 year  operator+(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 year  operator+(const years& x, const year&  y) NOEXCEPT;
+CONSTCD11 year  operator-(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 years operator-(const year&  x, const year&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y);
+
+// weekday
+
+class weekday
+{
+    unsigned char wd_;
+public:
+    weekday() = default;
+    explicit CONSTCD11 weekday(unsigned wd) NOEXCEPT;
+    CONSTCD14 weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD14 explicit weekday(const local_days& dp) NOEXCEPT;
+
+    CONSTCD14 weekday& operator++()    NOEXCEPT;
+    CONSTCD14 weekday  operator++(int) NOEXCEPT;
+    CONSTCD14 weekday& operator--()    NOEXCEPT;
+    CONSTCD14 weekday  operator--(int) NOEXCEPT;
+
+    CONSTCD14 weekday& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 weekday& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    CONSTCD11 unsigned c_encoding() const NOEXCEPT;
+    CONSTCD11 unsigned iso_encoding() const NOEXCEPT;
+
+    CONSTCD11 weekday_indexed operator[](unsigned index) const NOEXCEPT;
+    CONSTCD11 weekday_last    operator[](last_spec)      const NOEXCEPT;
+
+private:
+    static CONSTCD14 unsigned char weekday_from_days(int z) NOEXCEPT;
+
+    friend CONSTCD11 bool operator==(const weekday& x, const weekday& y) NOEXCEPT;
+    friend CONSTCD14 days operator-(const weekday& x, const weekday& y) NOEXCEPT;
+    friend CONSTCD14 weekday operator+(const weekday& x, const days& y) NOEXCEPT;
+    template<class CharT, class Traits>
+        friend std::basic_ostream<CharT, Traits>&
+            operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd);
+    friend class weekday_indexed;
+};
+
+CONSTCD11 bool operator==(const weekday& x, const weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday& x, const weekday& y) NOEXCEPT;
+
+CONSTCD14 weekday operator+(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 weekday operator+(const days&    x, const weekday& y) NOEXCEPT;
+CONSTCD14 weekday operator-(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 days    operator-(const weekday& x, const weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd);
+
+// weekday_indexed
+
+class weekday_indexed
+{
+    unsigned char wd_    : 4;
+    unsigned char index_ : 4;
+
+public:
+    weekday_indexed() = default;
+    CONSTCD11 weekday_indexed(const date::weekday& wd, unsigned index) NOEXCEPT;
+
+    CONSTCD11 date::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi);
+
+// weekday_last
+
+class weekday_last
+{
+    date::weekday wd_;
+
+public:
+    explicit CONSTCD11 weekday_last(const date::weekday& wd) NOEXCEPT;
+
+    CONSTCD11 date::weekday weekday() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl);
+
+namespace detail
+{
+
+struct unspecified_month_disambiguator {};
+
+}  // namespace detail
+
+// year_month
+
+class year_month
+{
+    date::year  y_;
+    date::month m_;
+
+public:
+    year_month() = default;
+    CONSTCD11 year_month(const date::year& y, const date::month& m) NOEXCEPT;
+
+    CONSTCD11 date::year  year()  const NOEXCEPT;
+    CONSTCD11 date::month month() const NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month& operator+=(const months& dm) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month& operator-=(const months& dm) NOEXCEPT;
+    CONSTCD14 year_month& operator+=(const years& dy) NOEXCEPT;
+    CONSTCD14 year_month& operator-=(const years& dy) NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month& x, const year_month& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month operator+(const year_month& ym, const months& dm) NOEXCEPT;
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month operator+(const months& dm, const year_month& ym) NOEXCEPT;
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month operator-(const year_month& ym, const months& dm) NOEXCEPT;
+
+CONSTCD11 months operator-(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 year_month operator+(const year_month& ym, const years& dy) NOEXCEPT;
+CONSTCD11 year_month operator+(const years& dy, const year_month& ym) NOEXCEPT;
+CONSTCD11 year_month operator-(const year_month& ym, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym);
+
+// month_day
+
+class month_day
+{
+    date::month m_;
+    date::day   d_;
+
+public:
+    month_day() = default;
+    CONSTCD11 month_day(const date::month& m, const date::day& d) NOEXCEPT;
+
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 date::day   day() const NOEXCEPT;
+
+    CONSTCD14 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day& x, const month_day& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md);
+
+// month_day_last
+
+class month_day_last
+{
+    date::month m_;
+
+public:
+    CONSTCD11 explicit month_day_last(const date::month& m) NOEXCEPT;
+
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl);
+
+// month_weekday
+
+class month_weekday
+{
+    date::month           m_;
+    date::weekday_indexed wdi_;
+public:
+    CONSTCD11 month_weekday(const date::month& m,
+                            const date::weekday_indexed& wdi) NOEXCEPT;
+
+    CONSTCD11 date::month           month()           const NOEXCEPT;
+    CONSTCD11 date::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd);
+
+// month_weekday_last
+
+class month_weekday_last
+{
+    date::month        m_;
+    date::weekday_last wdl_;
+
+public:
+    CONSTCD11 month_weekday_last(const date::month& m,
+                                 const date::weekday_last& wd) NOEXCEPT;
+
+    CONSTCD11 date::month        month()        const NOEXCEPT;
+    CONSTCD11 date::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl);
+
+// class year_month_day
+
+class year_month_day
+{
+    date::year  y_;
+    date::month m_;
+    date::day   d_;
+
+public:
+    year_month_day() = default;
+    CONSTCD11 year_month_day(const date::year& y, const date::month& m,
+                             const date::day& d) NOEXCEPT;
+    CONSTCD14 year_month_day(const year_month_day_last& ymdl) NOEXCEPT;
+
+    CONSTCD14 year_month_day(sys_days dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_day(local_days dp) NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_day& operator+=(const months& m) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_day& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 date::year  year()  const NOEXCEPT;
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 date::day   day()   const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_month_day from_days(days dp) NOEXCEPT;
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month_day operator+(const year_month_day& ymd, const months& dm) NOEXCEPT;
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month_day operator+(const months& dm, const year_month_day& ymd) NOEXCEPT;
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month_day operator-(const year_month_day& ymd, const months& dm) NOEXCEPT;
+CONSTCD11 year_month_day operator+(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+CONSTCD11 year_month_day operator+(const years& dy, const year_month_day& ymd)  NOEXCEPT;
+CONSTCD11 year_month_day operator-(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd);
+
+// year_month_day_last
+
+class year_month_day_last
+{
+    date::year           y_;
+    date::month_day_last mdl_;
+
+public:
+    CONSTCD11 year_month_day_last(const date::year& y,
+                                  const date::month_day_last& mdl) NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_day_last& operator+=(const months& m) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_day_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 date::year           year()           const NOEXCEPT;
+    CONSTCD11 date::month          month()          const NOEXCEPT;
+    CONSTCD11 date::month_day_last month_day_last() const NOEXCEPT;
+    CONSTCD14 date::day            day()            const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator< (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator> (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl);
+
+// year_month_weekday
+
+class year_month_weekday
+{
+    date::year            y_;
+    date::month           m_;
+    date::weekday_indexed wdi_;
+
+public:
+    year_month_weekday() = default;
+    CONSTCD11 year_month_weekday(const date::year& y, const date::month& m,
+                                   const date::weekday_indexed& wdi) NOEXCEPT;
+    CONSTCD14 year_month_weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_weekday(const local_days& dp) NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_weekday& operator+=(const months& m) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_weekday& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 date::year year() const NOEXCEPT;
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 date::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 date::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_month_weekday from_days(days dp) NOEXCEPT;
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi);
+
+// year_month_weekday_last
+
+class year_month_weekday_last
+{
+    date::year y_;
+    date::month m_;
+    date::weekday_last wdl_;
+
+public:
+    CONSTCD11 year_month_weekday_last(const date::year& y, const date::month& m,
+                                      const date::weekday_last& wdl) NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_weekday_last& operator+=(const months& m) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_weekday_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 date::year year() const NOEXCEPT;
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 date::weekday weekday() const NOEXCEPT;
+    CONSTCD11 date::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+private:
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+CONSTCD11
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl);
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11 date::day  operator "" _d(unsigned long long d) NOEXCEPT;
+CONSTCD11 date::year operator "" _y(unsigned long long y) NOEXCEPT;
+
+}  // inline namespace literals
+#endif // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+// CONSTDATA date::month January{1};
+// CONSTDATA date::month February{2};
+// CONSTDATA date::month March{3};
+// CONSTDATA date::month April{4};
+// CONSTDATA date::month May{5};
+// CONSTDATA date::month June{6};
+// CONSTDATA date::month July{7};
+// CONSTDATA date::month August{8};
+// CONSTDATA date::month September{9};
+// CONSTDATA date::month October{10};
+// CONSTDATA date::month November{11};
+// CONSTDATA date::month December{12};
+//
+// CONSTDATA date::weekday Sunday{0u};
+// CONSTDATA date::weekday Monday{1u};
+// CONSTDATA date::weekday Tuesday{2u};
+// CONSTDATA date::weekday Wednesday{3u};
+// CONSTDATA date::weekday Thursday{4u};
+// CONSTDATA date::weekday Friday{5u};
+// CONSTDATA date::weekday Saturday{6u};
+
+#if HAS_VOID_T
+
+template <class T, class = std::void_t<>>
+struct is_clock
+    : std::false_type
+{};
+
+template <class T>
+struct is_clock<T, std::void_t<decltype(T::now()), typename T::rep, typename T::period,
+                               typename T::duration, typename T::time_point,
+                               decltype(T::is_steady)>>
+    : std::true_type
+{};
+
+template<class T> inline constexpr bool is_clock_v = is_clock<T>::value;
+
+#endif  // HAS_VOID_T
+
+//----------------+
+// Implementation |
+//----------------+
+
+// utilities
+namespace detail {
+
+template<class CharT, class Traits = std::char_traits<CharT>>
+class save_istream
+{
+protected:
+    std::basic_ios<CharT, Traits>& is_;
+    CharT fill_;
+    std::ios::fmtflags flags_;
+    std::streamsize precision_;
+    std::streamsize width_;
+    std::basic_ostream<CharT, Traits>* tie_;
+    std::locale loc_;
+
+public:
+    ~save_istream()
+    {
+        is_.fill(fill_);
+        is_.flags(flags_);
+        is_.precision(precision_);
+        is_.width(width_);
+        is_.imbue(loc_);
+        is_.tie(tie_);
+    }
+
+    save_istream(const save_istream&) = delete;
+    save_istream& operator=(const save_istream&) = delete;
+
+    explicit save_istream(std::basic_ios<CharT, Traits>& is)
+        : is_(is)
+        , fill_(is.fill())
+        , flags_(is.flags())
+        , precision_(is.precision())
+        , width_(is.width(0))
+        , tie_(is.tie(nullptr))
+        , loc_(is.getloc())
+        {
+            if (tie_ != nullptr)
+                tie_->flush();
+        }
+};
+
+template<class CharT, class Traits = std::char_traits<CharT>>
+class save_ostream
+    : private save_istream<CharT, Traits>
+{
+public:
+    ~save_ostream()
+    {
+        if ((this->flags_ & std::ios::unitbuf) &&
+#if HAS_UNCAUGHT_EXCEPTIONS
+                std::uncaught_exceptions() == 0 &&
+#else
+                !std::uncaught_exception() &&
+#endif
+                this->is_.good())
+            this->is_.rdbuf()->pubsync();
+    }
+
+    save_ostream(const save_ostream&) = delete;
+    save_ostream& operator=(const save_ostream&) = delete;
+
+    explicit save_ostream(std::basic_ios<CharT, Traits>& os)
+        : save_istream<CharT, Traits>(os)
+        {
+        }
+};
+
+template <class T>
+struct choose_trunc_type
+{
+    static const int digits = std::numeric_limits<T>::digits;
+    using type = typename std::conditional
+                 <
+                     digits < 32,
+                     std::int32_t,
+                     typename std::conditional
+                     <
+                         digits < 64,
+                         std::int64_t,
+#ifdef __SIZEOF_INT128__
+                         __int128
+#else
+                         std::int64_t
+#endif
+                     >::type
+                 >::type;
+};
+
+template <class T>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    !std::chrono::treat_as_floating_point<T>::value,
+    T
+>::type
+trunc(T t) NOEXCEPT
+{
+    return t;
+}
+
+template <class T>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    std::chrono::treat_as_floating_point<T>::value,
+    T
+>::type
+trunc(T t) NOEXCEPT
+{
+    using std::numeric_limits;
+    using I = typename choose_trunc_type<T>::type;
+    CONSTDATA auto digits = numeric_limits<T>::digits;
+    static_assert(digits < numeric_limits<I>::digits, "");
+    CONSTDATA auto max = I{1} << (digits-1);
+    CONSTDATA auto min = -max;
+    const auto negative = t < T{0};
+    if (min <= t && t <= max && t != 0 && t == t)
+    {
+        t = static_cast<T>(static_cast<I>(t));
+        if (t == 0 && negative)
+            t = -t;
+    }
+    return t;
+}
+
+template <std::intmax_t Xp, std::intmax_t Yp>
+struct static_gcd
+{
+    static const std::intmax_t value = static_gcd<Yp, Xp % Yp>::value;
+};
+
+template <std::intmax_t Xp>
+struct static_gcd<Xp, 0>
+{
+    static const std::intmax_t value = Xp;
+};
+
+template <>
+struct static_gcd<0, 0>
+{
+    static const std::intmax_t value = 1;
+};
+
+template <class R1, class R2>
+struct no_overflow
+{
+private:
+    static const std::intmax_t gcd_n1_n2 = static_gcd<R1::num, R2::num>::value;
+    static const std::intmax_t gcd_d1_d2 = static_gcd<R1::den, R2::den>::value;
+    static const std::intmax_t n1 = R1::num / gcd_n1_n2;
+    static const std::intmax_t d1 = R1::den / gcd_d1_d2;
+    static const std::intmax_t n2 = R2::num / gcd_n1_n2;
+    static const std::intmax_t d2 = R2::den / gcd_d1_d2;
+#ifdef __cpp_constexpr
+    static const std::intmax_t max = std::numeric_limits<std::intmax_t>::max();
+#else
+    static const std::intmax_t max = LLONG_MAX;
+#endif
+
+    template <std::intmax_t Xp, std::intmax_t Yp, bool overflow>
+    struct mul    // overflow == false
+    {
+        static const std::intmax_t value = Xp * Yp;
+    };
+
+    template <std::intmax_t Xp, std::intmax_t Yp>
+    struct mul<Xp, Yp, true>
+    {
+        static const std::intmax_t value = 1;
+    };
+
+public:
+    static const bool value = (n1 <= max / d2) && (n2 <= max / d1);
+    typedef std::ratio<mul<n1, d2, !value>::value,
+                       mul<n2, d1, !value>::value> type;
+};
+
+}  // detail
+
+// trunc towards zero
+template <class To, class Rep, class Period>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    detail::no_overflow<Period, typename To::period>::value,
+    To
+>::type
+trunc(const std::chrono::duration<Rep, Period>& d)
+{
+    return To{detail::trunc(std::chrono::duration_cast<To>(d).count())};
+}
+
+template <class To, class Rep, class Period>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    !detail::no_overflow<Period, typename To::period>::value,
+    To
+>::type
+trunc(const std::chrono::duration<Rep, Period>& d)
+{
+    using std::chrono::duration_cast;
+    using std::chrono::duration;
+    using rep = typename std::common_type<Rep, typename To::rep>::type;
+    return To{detail::trunc(duration_cast<To>(duration_cast<duration<rep>>(d)).count())};
+}
+
+#ifndef HAS_CHRONO_ROUNDING
+#  if defined(_MSC_FULL_VER) && (_MSC_FULL_VER >= 190023918 || (_MSC_FULL_VER >= 190000000 && defined (__clang__)))
+#    define HAS_CHRONO_ROUNDING 1
+#  elif defined(__cpp_lib_chrono) && __cplusplus > 201402 && __cpp_lib_chrono >= 201510
+#    define HAS_CHRONO_ROUNDING 1
+#  elif defined(_LIBCPP_VERSION) && __cplusplus > 201402 && _LIBCPP_VERSION >= 3800
+#    define HAS_CHRONO_ROUNDING 1
+#  else
+#    define HAS_CHRONO_ROUNDING 0
+#  endif
+#endif  // HAS_CHRONO_ROUNDING
+
+#if HAS_CHRONO_ROUNDING == 0
+
+// round down
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    detail::no_overflow<Period, typename To::period>::value,
+    To
+>::type
+floor(const std::chrono::duration<Rep, Period>& d)
+{
+    auto t = trunc<To>(d);
+    if (t > d)
+        return t - To{1};
+    return t;
+}
+
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    !detail::no_overflow<Period, typename To::period>::value,
+    To
+>::type
+floor(const std::chrono::duration<Rep, Period>& d)
+{
+    using rep = typename std::common_type<Rep, typename To::rep>::type;
+    return floor<To>(floor<std::chrono::duration<rep>>(d));
+}
+
+// round to nearest, to even on tie
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+To
+round(const std::chrono::duration<Rep, Period>& d)
+{
+    auto t0 = floor<To>(d);
+    auto t1 = t0 + To{1};
+    if (t1 == To{0} && t0 < To{0})
+        t1 = -t1;
+    auto diff0 = d - t0;
+    auto diff1 = t1 - d;
+    if (diff0 == diff1)
+    {
+        if (t0 - trunc<To>(t0/2)*2 == To{0})
+            return t0;
+        return t1;
+    }
+    if (diff0 < diff1)
+        return t0;
+    return t1;
+}
+
+// round up
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+To
+ceil(const std::chrono::duration<Rep, Period>& d)
+{
+    auto t = trunc<To>(d);
+    if (t < d)
+        return t + To{1};
+    return t;
+}
+
+template <class Rep, class Period,
+          class = typename std::enable_if
+          <
+              std::numeric_limits<Rep>::is_signed
+          >::type>
+CONSTCD11
+std::chrono::duration<Rep, Period>
+abs(std::chrono::duration<Rep, Period> d)
+{
+    return d >= d.zero() ? d : static_cast<decltype(d)>(-d);
+}
+
+// round down
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+floor(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{date::floor<To>(tp.time_since_epoch())};
+}
+
+// round to nearest, to even on tie
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+round(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{round<To>(tp.time_since_epoch())};
+}
+
+// round up
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+ceil(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{ceil<To>(tp.time_since_epoch())};
+}
+
+#else  // HAS_CHRONO_ROUNDING == 1
+
+using std::chrono::floor;
+using std::chrono::ceil;
+using std::chrono::round;
+using std::chrono::abs;
+
+#endif  // HAS_CHRONO_ROUNDING
+
+namespace detail
+{
+
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    !std::chrono::treat_as_floating_point<typename To::rep>::value,
+    To
+>::type
+round_i(const std::chrono::duration<Rep, Period>& d)
+{
+    return round<To>(d);
+}
+
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    std::chrono::treat_as_floating_point<typename To::rep>::value,
+    To
+>::type
+round_i(const std::chrono::duration<Rep, Period>& d)
+{
+    return d;
+}
+
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+round_i(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{round_i<To>(tp.time_since_epoch())};
+}
+
+}  // detail
+
+// trunc towards zero
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+trunc(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{trunc<To>(tp.time_since_epoch())};
+}
+
+// day
+
+CONSTCD11 inline day::day(unsigned d) NOEXCEPT : d_(static_cast<decltype(d_)>(d)) {}
+CONSTCD14 inline day& day::operator++() NOEXCEPT {++d_; return *this;}
+CONSTCD14 inline day day::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline day& day::operator--() NOEXCEPT {--d_; return *this;}
+CONSTCD14 inline day day::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline day& day::operator+=(const days& d) NOEXCEPT {*this = *this + d; return *this;}
+CONSTCD14 inline day& day::operator-=(const days& d) NOEXCEPT {*this = *this - d; return *this;}
+CONSTCD11 inline day::operator unsigned() const NOEXCEPT {return d_;}
+CONSTCD11 inline bool day::ok() const NOEXCEPT {return 1 <= d_ && d_ <= 31;}
+
+CONSTCD11
+inline
+bool
+operator==(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const day& x, const day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const day& x, const day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+days
+operator-(const day& x, const day& y) NOEXCEPT
+{
+    return days{static_cast<days::rep>(static_cast<unsigned>(x)
+                                     - static_cast<unsigned>(y))};
+}
+
+CONSTCD11
+inline
+day
+operator+(const day& x, const days& y) NOEXCEPT
+{
+    return day{static_cast<unsigned>(x) + static_cast<unsigned>(y.count())};
+}
+
+CONSTCD11
+inline
+day
+operator+(const days& x, const day& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+day
+operator-(const day& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const day& d)
+{
+    detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os.width(2);
+    os << static_cast<unsigned>(d);
+    return os;
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d)
+{
+    detail::low_level_fmt(os, d);
+    if (!d.ok())
+        os << " is not a valid day";
+    return os;
+}
+
+// month
+
+CONSTCD11 inline month::month(unsigned m) NOEXCEPT : m_(static_cast<decltype(m_)>(m)) {}
+CONSTCD14 inline month& month::operator++() NOEXCEPT {*this += months{1}; return *this;}
+CONSTCD14 inline month month::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline month& month::operator--() NOEXCEPT {*this -= months{1}; return *this;}
+CONSTCD14 inline month month::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+month&
+month::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+month&
+month::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD11 inline month::operator unsigned() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month::ok() const NOEXCEPT {return 1 <= m_ && m_ <= 12;}
+
+CONSTCD11
+inline
+bool
+operator==(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month& x, const month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month& x, const month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD14
+inline
+months
+operator-(const month& x, const month& y) NOEXCEPT
+{
+    auto const d = static_cast<unsigned>(x) - static_cast<unsigned>(y);
+    return months(d <= 11 ? d : d + 12);
+}
+
+CONSTCD14
+inline
+month
+operator+(const month& x, const months& y) NOEXCEPT
+{
+    auto const mu = static_cast<long long>(static_cast<unsigned>(x)) + y.count() - 1;
+    auto const yr = (mu >= 0 ? mu : mu-11) / 12;
+    return month{static_cast<unsigned>(mu - yr * 12 + 1)};
+}
+
+CONSTCD14
+inline
+month
+operator+(const months& x, const month& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+month
+operator-(const month& x, const months& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month& m)
+{
+    if (m.ok())
+    {
+        CharT fmt[] = {'%', 'b', 0};
+        os << format(os.getloc(), fmt, m);
+    }
+    else
+        os << static_cast<unsigned>(m);
+    return os;
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m)
+{
+    detail::low_level_fmt(os, m);
+    if (!m.ok())
+        os << " is not a valid month";
+    return os;
+}
+
+// year
+
+CONSTCD11 inline year::year(int y) NOEXCEPT : y_(static_cast<decltype(y_)>(y)) {}
+CONSTCD14 inline year& year::operator++() NOEXCEPT {++y_; return *this;}
+CONSTCD14 inline year year::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline year& year::operator--() NOEXCEPT {--y_; return *this;}
+CONSTCD14 inline year year::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline year& year::operator+=(const years& y) NOEXCEPT {*this = *this + y; return *this;}
+CONSTCD14 inline year& year::operator-=(const years& y) NOEXCEPT {*this = *this - y; return *this;}
+CONSTCD11 inline year year::operator-() const NOEXCEPT {return year{-y_};}
+CONSTCD11 inline year year::operator+() const NOEXCEPT {return *this;}
+
+CONSTCD11
+inline
+bool
+year::is_leap() const NOEXCEPT
+{
+    return y_ % 4 == 0 && (y_ % 100 != 0 || y_ % 400 == 0);
+}
+
+CONSTCD11 inline year::operator int() const NOEXCEPT {return y_;}
+
+CONSTCD11
+inline
+bool
+year::ok() const NOEXCEPT
+{
+    return y_ != std::numeric_limits<short>::min();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) == static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) < static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year& x, const year& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year& x, const year& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+years
+operator-(const year& x, const year& y) NOEXCEPT
+{
+    return years{static_cast<int>(x) - static_cast<int>(y)};
+}
+
+CONSTCD11
+inline
+year
+operator+(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) + y.count()};
+}
+
+CONSTCD11
+inline
+year
+operator+(const years& x, const year& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+year
+operator-(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) - y.count()};
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const year& y)
+{
+    detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::internal);
+    os.width(4 + (y < year{0}));
+    os.imbue(std::locale::classic());
+    os << static_cast<int>(y);
+    return os;
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y)
+{
+    detail::low_level_fmt(os, y);
+    if (!y.ok())
+        os << " is not a valid year";
+    return os;
+}
+
+// weekday
+
+CONSTCD14
+inline
+unsigned char
+weekday::weekday_from_days(int z) NOEXCEPT
+{
+    auto u = static_cast<unsigned>(z);
+    return static_cast<unsigned char>(z >= -4 ? (u+4) % 7 : u % 7);
+}
+
+CONSTCD11
+inline
+weekday::weekday(unsigned wd) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(wd != 7 ? wd : 0))
+    {}
+
+CONSTCD14
+inline
+weekday::weekday(const sys_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD14
+inline
+weekday::weekday(const local_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD14 inline weekday& weekday::operator++() NOEXCEPT {*this += days{1}; return *this;}
+CONSTCD14 inline weekday weekday::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline weekday& weekday::operator--() NOEXCEPT {*this -= days{1}; return *this;}
+CONSTCD14 inline weekday weekday::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator+=(const days& d) NOEXCEPT
+{
+    *this = *this + d;
+    return *this;
+}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator-=(const days& d) NOEXCEPT
+{
+    *this = *this - d;
+    return *this;
+}
+
+CONSTCD11 inline bool weekday::ok() const NOEXCEPT {return wd_ <= 6;}
+
+CONSTCD11
+inline
+unsigned weekday::c_encoding() const NOEXCEPT
+{
+    return unsigned{wd_};
+}
+
+CONSTCD11
+inline
+unsigned weekday::iso_encoding() const NOEXCEPT
+{
+    return unsigned{((wd_ == 0u) ? 7u : wd_)};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return x.wd_ == y.wd_;
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD14
+inline
+days
+operator-(const weekday& x, const weekday& y) NOEXCEPT
+{
+    auto const wdu = x.wd_ - y.wd_;
+    auto const wk = (wdu >= 0 ? wdu : wdu-6) / 7;
+    return days{wdu - wk * 7};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const weekday& x, const days& y) NOEXCEPT
+{
+    auto const wdu = static_cast<long long>(static_cast<unsigned>(x.wd_)) + y.count();
+    auto const wk = (wdu >= 0 ? wdu : wdu-6) / 7;
+    return weekday{static_cast<unsigned>(wdu - wk * 7)};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const days& x, const weekday& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+weekday
+operator-(const weekday& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const weekday& wd)
+{
+    if (wd.ok())
+    {
+        CharT fmt[] = {'%', 'a', 0};
+        os << format(fmt, wd);
+    }
+    else
+        os << wd.c_encoding();
+    return os;
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd)
+{
+    detail::low_level_fmt(os, wd);
+    if (!wd.ok())
+        os << " is not a valid weekday";
+    return os;
+}
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11
+inline
+date::day
+operator "" _d(unsigned long long d) NOEXCEPT
+{
+    return date::day{static_cast<unsigned>(d)};
+}
+
+CONSTCD11
+inline
+date::year
+operator "" _y(unsigned long long y) NOEXCEPT
+{
+    return date::year(static_cast<int>(y));
+}
+#endif  // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+CONSTDATA date::last_spec last{};
+
+CONSTDATA date::month jan{1};
+CONSTDATA date::month feb{2};
+CONSTDATA date::month mar{3};
+CONSTDATA date::month apr{4};
+CONSTDATA date::month may{5};
+CONSTDATA date::month jun{6};
+CONSTDATA date::month jul{7};
+CONSTDATA date::month aug{8};
+CONSTDATA date::month sep{9};
+CONSTDATA date::month oct{10};
+CONSTDATA date::month nov{11};
+CONSTDATA date::month dec{12};
+
+CONSTDATA date::weekday sun{0u};
+CONSTDATA date::weekday mon{1u};
+CONSTDATA date::weekday tue{2u};
+CONSTDATA date::weekday wed{3u};
+CONSTDATA date::weekday thu{4u};
+CONSTDATA date::weekday fri{5u};
+CONSTDATA date::weekday sat{6u};
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+}  // inline namespace literals
+#endif
+
+CONSTDATA date::month January{1};
+CONSTDATA date::month February{2};
+CONSTDATA date::month March{3};
+CONSTDATA date::month April{4};
+CONSTDATA date::month May{5};
+CONSTDATA date::month June{6};
+CONSTDATA date::month July{7};
+CONSTDATA date::month August{8};
+CONSTDATA date::month September{9};
+CONSTDATA date::month October{10};
+CONSTDATA date::month November{11};
+CONSTDATA date::month December{12};
+
+CONSTDATA date::weekday Monday{1};
+CONSTDATA date::weekday Tuesday{2};
+CONSTDATA date::weekday Wednesday{3};
+CONSTDATA date::weekday Thursday{4};
+CONSTDATA date::weekday Friday{5};
+CONSTDATA date::weekday Saturday{6};
+CONSTDATA date::weekday Sunday{7};
+
+// weekday_indexed
+
+CONSTCD11
+inline
+weekday
+weekday_indexed::weekday() const NOEXCEPT
+{
+    return date::weekday{static_cast<unsigned>(wd_)};
+}
+
+CONSTCD11 inline unsigned weekday_indexed::index() const NOEXCEPT {return index_;}
+
+CONSTCD11
+inline
+bool
+weekday_indexed::ok() const NOEXCEPT
+{
+    return weekday().ok() && 1 <= index_ && index_ <= 5;
+}
+
+#ifdef __GNUC__
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wconversion"
+#endif  // __GNUC__
+
+CONSTCD11
+inline
+weekday_indexed::weekday_indexed(const date::weekday& wd, unsigned index) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(static_cast<unsigned>(wd.wd_)))
+    , index_(static_cast<decltype(index_)>(index))
+    {}
+
+#ifdef __GNUC__
+#  pragma GCC diagnostic pop
+#endif  // __GNUC__
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi)
+{
+    return low_level_fmt(os, wdi.weekday()) << '[' << wdi.index() << ']';
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi)
+{
+    detail::low_level_fmt(os, wdi);
+    if (!wdi.ok())
+        os << " is not a valid weekday_indexed";
+    return os;
+}
+
+CONSTCD11
+inline
+weekday_indexed
+weekday::operator[](unsigned index) const NOEXCEPT
+{
+    return {*this, index};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday() && x.index() == y.index();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+// weekday_last
+
+CONSTCD11 inline date::weekday weekday_last::weekday() const NOEXCEPT {return wd_;}
+CONSTCD11 inline bool weekday_last::ok() const NOEXCEPT {return wd_.ok();}
+CONSTCD11 inline weekday_last::weekday_last(const date::weekday& wd) NOEXCEPT : wd_(wd) {}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl)
+{
+    return low_level_fmt(os, wdl.weekday()) << "[last]";
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl)
+{
+    detail::low_level_fmt(os, wdl);
+    if (!wdl.ok())
+        os << " is not a valid weekday_last";
+    return os;
+}
+
+CONSTCD11
+inline
+weekday_last
+weekday::operator[](last_spec) const NOEXCEPT
+{
+    return weekday_last{*this};
+}
+
+// year_month
+
+CONSTCD11
+inline
+year_month::year_month(const date::year& y, const date::month& m) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    {}
+
+CONSTCD11 inline year year_month::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool year_month::ok() const NOEXCEPT {return y_.ok() && m_.ok();}
+
+template<class>
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const months& dm) NOEXCEPT
+{
+    *this = *this + dm;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const months& dm) NOEXCEPT
+{
+    *this = *this - dm;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const years& dy) NOEXCEPT
+{
+    *this = *this + dy;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const years& dy) NOEXCEPT
+{
+    *this = *this - dy;
+    return *this;
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class>
+CONSTCD14
+inline
+year_month
+operator+(const year_month& ym, const months& dm) NOEXCEPT
+{
+    auto dmi = static_cast<int>(static_cast<unsigned>(ym.month())) - 1 + dm.count();
+    auto dy = (dmi >= 0 ? dmi : dmi-11) / 12;
+    dmi = dmi - dy * 12 + 1;
+    return (ym.year() + years(dy)) / month(static_cast<unsigned>(dmi));
+}
+
+template<class>
+CONSTCD14
+inline
+year_month
+operator+(const months& dm, const year_month& ym) NOEXCEPT
+{
+    return ym + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month
+operator-(const year_month& ym, const months& dm) NOEXCEPT
+{
+    return ym + -dm;
+}
+
+CONSTCD11
+inline
+months
+operator-(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return (x.year() - y.year()) +
+            months(static_cast<unsigned>(x.month()) - static_cast<unsigned>(y.month()));
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return (ym.year() + dy) / ym.month();
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const years& dy, const year_month& ym) NOEXCEPT
+{
+    return ym + dy;
+}
+
+CONSTCD11
+inline
+year_month
+operator-(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return ym + -dy;
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const year_month& ym)
+{
+    low_level_fmt(os, ym.year()) << '/';
+    return low_level_fmt(os, ym.month());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym)
+{
+    detail::low_level_fmt(os, ym);
+    if (!ym.ok())
+        os << " is not a valid year_month";
+    return os;
+}
+
+// month_day
+
+CONSTCD11
+inline
+month_day::month_day(const date::month& m, const date::day& d) NOEXCEPT
+    : m_(m)
+    , d_(d)
+    {}
+
+CONSTCD11 inline date::month month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline date::day month_day::day() const NOEXCEPT {return d_;}
+
+CONSTCD14
+inline
+bool
+month_day::ok() const NOEXCEPT
+{
+    CONSTDATA date::day d[] =
+    {
+        date::day(31), date::day(29), date::day(31),
+        date::day(30), date::day(31), date::day(30),
+        date::day(31), date::day(31), date::day(30),
+        date::day(31), date::day(30), date::day(31)
+    };
+    return m_.ok() && date::day{1} <= d_ && d_ <= d[static_cast<unsigned>(m_)-1];
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month_day& md)
+{
+    low_level_fmt(os, md.month()) << '/';
+    return low_level_fmt(os, md.day());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md)
+{
+    detail::low_level_fmt(os, md);
+    if (!md.ok())
+        os << " is not a valid month_day";
+    return os;
+}
+
+// month_day_last
+
+CONSTCD11 inline month month_day_last::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month_day_last::ok() const NOEXCEPT {return m_.ok();}
+CONSTCD11 inline month_day_last::month_day_last(const date::month& m) NOEXCEPT : m_(m) {}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() < y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl)
+{
+    return low_level_fmt(os, mdl.month()) << "/last";
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl)
+{
+    detail::low_level_fmt(os, mdl);
+    if (!mdl.ok())
+        os << " is not a valid month_day_last";
+    return os;
+}
+
+// month_weekday
+
+CONSTCD11
+inline
+month_weekday::month_weekday(const date::month& m,
+                             const date::weekday_indexed& wdi) NOEXCEPT
+    : m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD11 inline month month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_indexed
+month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday::ok() const NOEXCEPT
+{
+    return m_.ok() && wdi_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd)
+{
+    low_level_fmt(os, mwd.month()) << '/';
+    return low_level_fmt(os, mwd.weekday_indexed());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd)
+{
+    detail::low_level_fmt(os, mwd);
+    if (!mwd.ok())
+        os << " is not a valid month_weekday";
+    return os;
+}
+
+// month_weekday_last
+
+CONSTCD11
+inline
+month_weekday_last::month_weekday_last(const date::month& m,
+                                       const date::weekday_last& wdl) NOEXCEPT
+    : m_(m)
+    , wdl_(wdl)
+    {}
+
+CONSTCD11 inline month month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_last
+month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday_last::ok() const NOEXCEPT
+{
+    return m_.ok() && wdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl)
+{
+    low_level_fmt(os, mwdl.month()) << '/';
+    return low_level_fmt(os, mwdl.weekday_last());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl)
+{
+    detail::low_level_fmt(os, mwdl);
+    if (!mwdl.ok())
+        os << " is not a valid month_weekday_last";
+    return os;
+}
+
+// year_month_day_last
+
+CONSTCD11
+inline
+year_month_day_last::year_month_day_last(const date::year& y,
+                                         const date::month_day_last& mdl) NOEXCEPT
+    : y_(y)
+    , mdl_(mdl)
+    {}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_day_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day_last::month() const NOEXCEPT {return mdl_.month();}
+
+CONSTCD11
+inline
+month_day_last
+year_month_day_last::month_day_last() const NOEXCEPT
+{
+    return mdl_;
+}
+
+CONSTCD14
+inline
+day
+year_month_day_last::day() const NOEXCEPT
+{
+    CONSTDATA date::day d[] =
+    {
+        date::day(31), date::day(28), date::day(31),
+        date::day(30), date::day(31), date::day(30),
+        date::day(31), date::day(31), date::day(30),
+        date::day(31), date::day(30), date::day(31)
+    };
+    return (month() != February || !y_.is_leap()) && mdl_.ok() ?
+        d[static_cast<unsigned>(month()) - 1] : date::day{29};
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days(year()/month()/day());
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator local_days() const NOEXCEPT
+{
+    return local_days(year()/month()/day());
+}
+
+CONSTCD11
+inline
+bool
+year_month_day_last::ok() const NOEXCEPT
+{
+    return y_.ok() && mdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month_day_last() == y.month_day_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month_day_last() < y.month_day_last()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl)
+{
+    low_level_fmt(os, ymdl.year()) << '/';
+    return low_level_fmt(os, ymdl.month_day_last());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl)
+{
+    detail::low_level_fmt(os, ymdl);
+    if (!ymdl.ok())
+        os << " is not a valid year_month_day_last";
+    return os;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return (ymdl.year() / ymdl.month() + dm) / last;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return ymdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return {ymdl.year()+dy, ymdl.month_day_last()};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return ymdl + (-dy);
+}
+
+// year_month_day
+
+CONSTCD11
+inline
+year_month_day::year_month_day(const date::year& y, const date::month& m,
+                               const date::day& d) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , d_(d)
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(const year_month_day_last& ymdl) NOEXCEPT
+    : y_(ymdl.year())
+    , m_(ymdl.month())
+    , d_(ymdl.day())
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(sys_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(local_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD11 inline year year_month_day::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline day year_month_day::day() const NOEXCEPT {return d_;}
+
+template<class>
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD14
+inline
+days
+year_month_day::to_days() const NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+    auto const y = static_cast<int>(y_) - (m_ <= February);
+    auto const m = static_cast<unsigned>(m_);
+    auto const d = static_cast<unsigned>(d_);
+    auto const era = (y >= 0 ? y : y-399) / 400;
+    auto const yoe = static_cast<unsigned>(y - era * 400);       // [0, 399]
+    auto const doy = (153*(m > 2 ? m-3 : m+9) + 2)/5 + d-1;      // [0, 365]
+    auto const doe = yoe * 365 + yoe/4 - yoe/100 + doy;          // [0, 146096]
+    return days{era * 146097 + static_cast<int>(doe) - 719468};
+}
+
+CONSTCD14
+inline
+year_month_day::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_day::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_day::ok() const NOEXCEPT
+{
+    if (!(y_.ok() && m_.ok()))
+        return false;
+    return date::day{1} <= d_ && d_ <= (y_ / m_ / last).day();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()))));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd)
+{
+    detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os.imbue(std::locale::classic());
+    os << static_cast<int>(ymd.year()) << '-';
+    os.width(2);
+    os << static_cast<unsigned>(ymd.month()) << '-';
+    os.width(2);
+    os << static_cast<unsigned>(ymd.day());
+    if (!ymd.ok())
+        os << " is not a valid year_month_day";
+    return os;
+}
+
+CONSTCD14
+inline
+year_month_day
+year_month_day::from_days(days dp) NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+    auto const z = dp.count() + 719468;
+    auto const era = (z >= 0 ? z : z - 146096) / 146097;
+    auto const doe = static_cast<unsigned>(z - era * 146097);          // [0, 146096]
+    auto const yoe = (doe - doe/1460 + doe/36524 - doe/146096) / 365;  // [0, 399]
+    auto const y = static_cast<days::rep>(yoe) + era * 400;
+    auto const doy = doe - (365*yoe + yoe/4 - yoe/100);                // [0, 365]
+    auto const mp = (5*doy + 2)/153;                                   // [0, 11]
+    auto const d = doy - (153*mp+2)/5 + 1;                             // [1, 31]
+    auto const m = mp < 10 ? mp+3 : mp-9;                              // [1, 12]
+    return year_month_day{date::year{y + (m <= 2)}, date::month(m), date::day(d)};
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day
+operator+(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return (ymd.year() / ymd.month() + dm) / ymd.day();
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day
+operator+(const months& dm, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day
+operator-(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return ymd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return (ymd.year() + dy) / ymd.month() / ymd.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const years& dy, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dy;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator-(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return ymd + (-dy);
+}
+
+// year_month_weekday
+
+CONSTCD11
+inline
+year_month_weekday::year_month_weekday(const date::year& y, const date::month& m,
+                                       const date::weekday_indexed& wdi)
+        NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const sys_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const local_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday::weekday() const NOEXCEPT
+{
+    return wdi_.weekday();
+}
+
+CONSTCD11
+inline
+unsigned
+year_month_weekday::index() const NOEXCEPT
+{
+    return wdi_.index();
+}
+
+CONSTCD11
+inline
+weekday_indexed
+year_month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_weekday::ok() const NOEXCEPT
+{
+    if (!y_.ok() || !m_.ok() || !wdi_.weekday().ok() || wdi_.index() < 1)
+        return false;
+    if (wdi_.index() <= 4)
+        return true;
+    auto d2 = wdi_.weekday() - date::weekday(static_cast<sys_days>(y_/m_/1)) +
+                  days((wdi_.index()-1)*7 + 1);
+    return static_cast<unsigned>(d2.count()) <= static_cast<unsigned>((y_/m_/last).day());
+}
+
+CONSTCD14
+inline
+year_month_weekday
+year_month_weekday::from_days(days d) NOEXCEPT
+{
+    sys_days dp{d};
+    auto const wd = date::weekday(dp);
+    auto const ymd = year_month_day(dp);
+    return {ymd.year(), ymd.month(), wd[(static_cast<unsigned>(ymd.day())-1)/7+1]};
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday::to_days() const NOEXCEPT
+{
+    auto d = sys_days(y_/m_/1);
+    return (d + (wdi_.weekday() - date::weekday(d) + days{(wdi_.index()-1)*7})
+           ).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi)
+{
+    detail::low_level_fmt(os, ymwdi.year()) << '/';
+    detail::low_level_fmt(os, ymwdi.month()) << '/';
+    detail::low_level_fmt(os, ymwdi.weekday_indexed());
+    if (!ymwdi.ok())
+        os << " is not a valid year_month_weekday";
+    return os;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return (ymwd.year() / ymwd.month() + dm) / ymwd.weekday_indexed();
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return ymwd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return {ymwd.year()+dy, ymwd.month(), ymwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return ymwd + (-dy);
+}
+
+// year_month_weekday_last
+
+CONSTCD11
+inline
+year_month_weekday_last::year_month_weekday_last(const date::year& y,
+                                                 const date::month& m,
+                                                 const date::weekday_last& wdl) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdl_(wdl)
+    {}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday_last::weekday() const NOEXCEPT
+{
+    return wdl_.weekday();
+}
+
+CONSTCD11
+inline
+weekday_last
+year_month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD11
+inline
+bool
+year_month_weekday_last::ok() const NOEXCEPT
+{
+    return y_.ok() && m_.ok() && wdl_.ok();
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday_last::to_days() const NOEXCEPT
+{
+    auto const d = sys_days(y_/m_/last);
+    return (d - (date::weekday{d} - wdl_.weekday())).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl)
+{
+    detail::low_level_fmt(os, ymwdl.year()) << '/';
+    detail::low_level_fmt(os, ymwdl.month()) << '/';
+    detail::low_level_fmt(os, ymwdl.weekday_last());
+    if (!ymwdl.ok())
+        os << " is not a valid year_month_weekday_last";
+    return os;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return (ymwdl.year() / ymwdl.month() + dm) / ymwdl.weekday_last();
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return ymwdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return {ymwdl.year()+dy, ymwdl.month(), ymwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return ymwdl + (-dy);
+}
+
+// year_month from operator/()
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, const month& m) NOEXCEPT
+{
+    return {y, m};
+}
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, int   m) NOEXCEPT
+{
+    return y / month(static_cast<unsigned>(m));
+}
+
+// month_day from operator/()
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, const day& d) NOEXCEPT
+{
+    return {m, d};
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const day& d, const month& m) NOEXCEPT
+{
+    return m / d;
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, int d) NOEXCEPT
+{
+    return m / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+month_day
+operator/(int m, const day& d) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / d;
+}
+
+CONSTCD11 inline month_day operator/(const day& d, int m) NOEXCEPT {return m / d;}
+
+// month_day_last from operator/()
+
+CONSTCD11
+inline
+month_day_last
+operator/(const month& m, last_spec) NOEXCEPT
+{
+    return month_day_last{m};
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, const month& m) NOEXCEPT
+{
+    return m/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(int m, last_spec) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m))/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, int m) NOEXCEPT
+{
+    return m/last;
+}
+
+// month_weekday from operator/()
+
+CONSTCD11
+inline
+month_weekday
+operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {m, wdi};
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(int m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, int m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+// month_weekday_last from operator/()
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const month& m, const weekday_last& wdl) NOEXCEPT
+{
+    return {m, wdl};
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, const month& m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(int m, const weekday_last& wdl) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, int m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+// year_month_day from operator/()
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, const day& d) NOEXCEPT
+{
+    return {ym.year(), ym.month(), d};
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, int d)  NOEXCEPT
+{
+    return ym / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year& y, const month_day& md) NOEXCEPT
+{
+    return y / md.month() / md.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(int y, const month_day& md) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, const year& y)  NOEXCEPT
+{
+    return y / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, int y) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+// year_month_day_last from operator/()
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year_month& ym, last_spec) NOEXCEPT
+{
+    return {ym.year(), month_day_last{ym.month()}};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year& y, const month_day_last& mdl) NOEXCEPT
+{
+    return {y, mdl};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(int y, const month_day_last& mdl) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, const year& y) NOEXCEPT
+{
+    return y / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, int y) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+// year_month_weekday from operator/()
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdi};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year& y, const month_weekday& mwd) NOEXCEPT
+{
+    return {y, mwd.month(), mwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(int y, const month_weekday& mwd) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, const year& y) NOEXCEPT
+{
+    return y / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, int y) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+// year_month_weekday_last from operator/()
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdl};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return {y, mwdl.month(), mwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(int y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT
+{
+    return y / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int y) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+template <class Duration>
+struct fields;
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const fields<Duration>& fds, const std::string* abbrev = nullptr,
+          const std::chrono::seconds* offset_sec = nullptr);
+
+template <class CharT, class Traits, class Duration, class Alloc>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            fields<Duration>& fds, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr);
+
+// hh_mm_ss
+
+namespace detail
+{
+
+struct undocumented {explicit undocumented() = default;};
+
+// width<n>::value is the number of fractional decimal digits in 1/n
+// width<0>::value and width<1>::value are defined to be 0
+// If 1/n takes more than 18 fractional decimal digits,
+//   the result is truncated to 19.
+// Example:  width<2>::value    ==  1
+// Example:  width<3>::value    == 19
+// Example:  width<4>::value    ==  2
+// Example:  width<10>::value   ==  1
+// Example:  width<1000>::value ==  3
+template <std::uint64_t n, std::uint64_t d, unsigned w = 0,
+          bool should_continue = n%d != 0 && (w < 19)>
+struct width
+{
+    static_assert(d > 0, "width called with zero denominator");
+    static CONSTDATA unsigned value = 1 + width<n%d*10, d, w+1>::value;
+};
+
+template <std::uint64_t n, std::uint64_t d, unsigned w>
+struct width<n, d, w, false>
+{
+    static CONSTDATA unsigned value = 0;
+};
+
+template <unsigned exp>
+struct static_pow10
+{
+private:
+    static CONSTDATA std::uint64_t h = static_pow10<exp/2>::value;
+public:
+    static CONSTDATA std::uint64_t value = h * h * (exp % 2 ? 10 : 1);
+};
+
+template <>
+struct static_pow10<0>
+{
+    static CONSTDATA std::uint64_t value = 1;
+};
+
+template <class Duration>
+class decimal_format_seconds
+{
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    using rep = typename CT::rep;
+    static unsigned CONSTDATA trial_width =
+        detail::width<CT::period::num, CT::period::den>::value;
+public:
+    static unsigned CONSTDATA width = trial_width < 19 ? trial_width : 6u;
+    using precision = std::chrono::duration<rep,
+                                            std::ratio<1, static_pow10<width>::value>>;
+
+private:
+    std::chrono::seconds s_;
+    precision            sub_s_;
+
+public:
+    CONSTCD11 decimal_format_seconds()
+        : s_()
+        , sub_s_()
+        {}
+
+    CONSTCD11 explicit decimal_format_seconds(const Duration& d) NOEXCEPT
+        : s_(std::chrono::duration_cast<std::chrono::seconds>(d))
+        , sub_s_(std::chrono::duration_cast<precision>(d - s_))
+        {}
+
+    CONSTCD14 std::chrono::seconds& seconds() NOEXCEPT {return s_;}
+    CONSTCD11 std::chrono::seconds seconds() const NOEXCEPT {return s_;}
+    CONSTCD11 precision subseconds() const NOEXCEPT {return sub_s_;}
+
+    CONSTCD14 precision to_duration() const NOEXCEPT
+    {
+        return s_ + sub_s_;
+    }
+
+    CONSTCD11 bool in_conventional_range() const NOEXCEPT
+    {
+        return sub_s_ < std::chrono::seconds{1} && s_ < std::chrono::minutes{1};
+    }
+
+    template <class CharT, class Traits>
+    friend
+    std::basic_ostream<CharT, Traits>&
+    operator<<(std::basic_ostream<CharT, Traits>& os, const decimal_format_seconds& x)
+    {
+        return x.print(os, std::chrono::treat_as_floating_point<rep>{});
+    }
+
+    template <class CharT, class Traits>
+    std::basic_ostream<CharT, Traits>&
+    print(std::basic_ostream<CharT, Traits>& os, std::true_type) const
+    {
+        date::detail::save_ostream<CharT, Traits> _(os);
+        std::chrono::duration<rep> d = s_ + sub_s_;
+        if (d < std::chrono::seconds{10})
+            os << '0';
+        os.precision(width+6);
+        os << std::fixed << d.count();
+        return os;
+    }
+
+    template <class CharT, class Traits>
+    std::basic_ostream<CharT, Traits>&
+    print(std::basic_ostream<CharT, Traits>& os, std::false_type) const
+    {
+        date::detail::save_ostream<CharT, Traits> _(os);
+        os.fill('0');
+        os.flags(std::ios::dec | std::ios::right);
+        os.width(2);
+        os << s_.count();
+        if (width > 0)
+        {
+#if !ONLY_C_LOCALE
+            os << std::use_facet<std::numpunct<CharT>>(os.getloc()).decimal_point();
+#else
+            os << '.';
+#endif
+            date::detail::save_ostream<CharT, Traits> _s(os);
+            os.imbue(std::locale::classic());
+            os.width(width);
+            os << sub_s_.count();
+        }
+        return os;
+    }
+};
+
+template <class Rep, class Period>
+inline
+CONSTCD11
+typename std::enable_if
+         <
+            std::numeric_limits<Rep>::is_signed,
+            std::chrono::duration<Rep, Period>
+         >::type
+abs(std::chrono::duration<Rep, Period> d)
+{
+    return d >= d.zero() ? +d : -d;
+}
+
+template <class Rep, class Period>
+inline
+CONSTCD11
+typename std::enable_if
+         <
+            !std::numeric_limits<Rep>::is_signed,
+            std::chrono::duration<Rep, Period>
+         >::type
+abs(std::chrono::duration<Rep, Period> d)
+{
+    return d;
+}
+
+}  // namespace detail
+
+template <class Duration>
+class hh_mm_ss
+{
+    using dfs = detail::decimal_format_seconds<typename std::common_type<Duration,
+                                               std::chrono::seconds>::type>;
+
+    std::chrono::hours h_;
+    std::chrono::minutes m_;
+    dfs s_;
+    bool neg_;
+
+public:
+    static unsigned CONSTDATA fractional_width = dfs::width;
+    using precision = typename dfs::precision;
+
+    CONSTCD11 hh_mm_ss() NOEXCEPT
+        : hh_mm_ss(Duration::zero())
+        {}
+
+    CONSTCD11 explicit hh_mm_ss(Duration d) NOEXCEPT
+        : h_(std::chrono::duration_cast<std::chrono::hours>(detail::abs(d)))
+        , m_(std::chrono::duration_cast<std::chrono::minutes>(detail::abs(d)) - h_)
+        , s_(detail::abs(d) - h_ - m_)
+        , neg_(d < Duration::zero())
+        {}
+
+    CONSTCD11 std::chrono::hours hours() const NOEXCEPT {return h_;}
+    CONSTCD11 std::chrono::minutes minutes() const NOEXCEPT {return m_;}
+    CONSTCD11 std::chrono::seconds seconds() const NOEXCEPT {return s_.seconds();}
+    CONSTCD14 std::chrono::seconds&
+        seconds(detail::undocumented) NOEXCEPT {return s_.seconds();}
+    CONSTCD11 precision subseconds() const NOEXCEPT {return s_.subseconds();}
+    CONSTCD11 bool is_negative() const NOEXCEPT {return neg_;}
+
+    CONSTCD11 explicit operator  precision()   const NOEXCEPT {return to_duration();}
+    CONSTCD11          precision to_duration() const NOEXCEPT
+        {return (s_.to_duration() + m_ + h_) * (1-2*neg_);}
+
+    CONSTCD11 bool in_conventional_range() const NOEXCEPT
+    {
+        return !neg_ && h_ < days{1} && m_ < std::chrono::hours{1} &&
+               s_.in_conventional_range();
+    }
+
+private:
+
+    template <class charT, class traits>
+    friend
+    std::basic_ostream<charT, traits>&
+    operator<<(std::basic_ostream<charT, traits>& os, hh_mm_ss const& tod)
+    {
+        if (tod.is_negative())
+            os << '-';
+        if (tod.h_ < std::chrono::hours{10})
+            os << '0';
+        os << tod.h_.count() << ':';
+        if (tod.m_ < std::chrono::minutes{10})
+            os << '0';
+        os << tod.m_.count() << ':' << tod.s_;
+        return os;
+    }
+
+    template <class CharT, class Traits, class Duration2>
+    friend
+    std::basic_ostream<CharT, Traits>&
+    date::to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const fields<Duration2>& fds, const std::string* abbrev,
+          const std::chrono::seconds* offset_sec);
+
+    template <class CharT, class Traits, class Duration2, class Alloc>
+    friend
+    std::basic_istream<CharT, Traits>&
+    date::from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+          fields<Duration2>& fds,
+          std::basic_string<CharT, Traits, Alloc>* abbrev, std::chrono::minutes* offset);
+};
+
+inline
+CONSTCD14
+bool
+is_am(std::chrono::hours const& h) NOEXCEPT
+{
+    using std::chrono::hours;
+    return hours{0} <= h && h < hours{12};
+}
+
+inline
+CONSTCD14
+bool
+is_pm(std::chrono::hours const& h) NOEXCEPT
+{
+    using std::chrono::hours;
+    return hours{12} <= h && h < hours{24};
+}
+
+inline
+CONSTCD14
+std::chrono::hours
+make12(std::chrono::hours h) NOEXCEPT
+{
+    using std::chrono::hours;
+    if (h < hours{12})
+    {
+        if (h == hours{0})
+            h = hours{12};
+    }
+    else
+    {
+        if (h != hours{12})
+            h = h - hours{12};
+    }
+    return h;
+}
+
+inline
+CONSTCD14
+std::chrono::hours
+make24(std::chrono::hours h, bool is_pm) NOEXCEPT
+{
+    using std::chrono::hours;
+    if (is_pm)
+    {
+        if (h != hours{12})
+            h = h + hours{12};
+    }
+    else if (h == hours{12})
+        h = hours{0};
+    return h;
+}
+
+template <class Duration>
+using time_of_day = hh_mm_ss<Duration>;
+
+template <class Rep, class Period>
+CONSTCD11
+inline
+hh_mm_ss<std::chrono::duration<Rep, Period>>
+make_time(const std::chrono::duration<Rep, Period>& d)
+{
+    return hh_mm_ss<std::chrono::duration<Rep, Period>>(d);
+}
+
+template <class CharT, class Traits, class Duration>
+inline
+typename std::enable_if
+<
+    !std::is_convertible<Duration, days>::value,
+    std::basic_ostream<CharT, Traits>&
+>::type
+operator<<(std::basic_ostream<CharT, Traits>& os, const sys_time<Duration>& tp)
+{
+    auto const dp = date::floor<days>(tp);
+    return os << year_month_day(dp) << ' ' << make_time(tp-dp);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const sys_days& dp)
+{
+    return os << year_month_day(dp);
+}
+
+template <class CharT, class Traits, class Duration>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const local_time<Duration>& ut)
+{
+    return (os << sys_time<Duration>{ut.time_since_epoch()});
+}
+
+namespace detail
+{
+
+template <class CharT, std::size_t N>
+class string_literal;
+
+template <class CharT1, class CharT2, std::size_t N1, std::size_t N2>
+inline
+CONSTCD14
+string_literal<typename std::conditional<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>::type,
+               N1 + N2 - 1>
+operator+(const string_literal<CharT1, N1>& x, const string_literal<CharT2, N2>& y) NOEXCEPT;
+
+template <class CharT, std::size_t N>
+class string_literal
+{
+    CharT p_[N];
+
+    CONSTCD11 string_literal() NOEXCEPT
+      : p_{}
+    {}
+
+public:
+    using const_iterator = const CharT*;
+
+    string_literal(string_literal const&) = default;
+    string_literal& operator=(string_literal const&) = delete;
+
+    template <std::size_t N1 = 2,
+              class = typename std::enable_if<N1 == N>::type>
+    CONSTCD11 string_literal(CharT c) NOEXCEPT
+        : p_{c}
+    {
+    }
+
+    template <std::size_t N1 = 3,
+              class = typename std::enable_if<N1 == N>::type>
+    CONSTCD11 string_literal(CharT c1, CharT c2) NOEXCEPT
+        : p_{c1, c2}
+    {
+    }
+
+    template <std::size_t N1 = 4,
+              class = typename std::enable_if<N1 == N>::type>
+    CONSTCD11 string_literal(CharT c1, CharT c2, CharT c3) NOEXCEPT
+        : p_{c1, c2, c3}
+    {
+    }
+
+    CONSTCD14 string_literal(const CharT(&a)[N]) NOEXCEPT
+        : p_{}
+    {
+        for (std::size_t i = 0; i < N; ++i)
+            p_[i] = a[i];
+    }
+
+    template <class U = CharT,
+              class = typename std::enable_if<(1 < sizeof(U))>::type>
+    CONSTCD14 string_literal(const char(&a)[N]) NOEXCEPT
+        : p_{}
+    {
+        for (std::size_t i = 0; i < N; ++i)
+            p_[i] = a[i];
+    }
+
+    template <class CharT2,
+              class = typename std::enable_if<!std::is_same<CharT2, CharT>::value>::type>
+    CONSTCD14 string_literal(string_literal<CharT2, N> const& a) NOEXCEPT
+        : p_{}
+    {
+        for (std::size_t i = 0; i < N; ++i)
+            p_[i] = a[i];
+    }
+
+    CONSTCD11 const CharT* data() const NOEXCEPT {return p_;}
+    CONSTCD11 std::size_t size() const NOEXCEPT {return N-1;}
+
+    CONSTCD11 const_iterator begin() const NOEXCEPT {return p_;}
+    CONSTCD11 const_iterator end()   const NOEXCEPT {return p_ + N-1;}
+
+    CONSTCD11 CharT const& operator[](std::size_t n) const NOEXCEPT
+    {
+        return p_[n];
+    }
+
+    template <class Traits>
+    friend
+    std::basic_ostream<CharT, Traits>&
+    operator<<(std::basic_ostream<CharT, Traits>& os, const string_literal& s)
+    {
+        return os << s.p_;
+    }
+
+    template <class CharT1, class CharT2, std::size_t N1, std::size_t N2>
+    friend
+    CONSTCD14
+    string_literal<typename std::conditional<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>::type,
+                   N1 + N2 - 1>
+    operator+(const string_literal<CharT1, N1>& x, const string_literal<CharT2, N2>& y) NOEXCEPT;
+};
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 3>
+operator+(const string_literal<CharT, 2>& x, const string_literal<CharT, 2>& y) NOEXCEPT
+{
+  return string_literal<CharT, 3>(x[0], y[0]);
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 4>
+operator+(const string_literal<CharT, 3>& x, const string_literal<CharT, 2>& y) NOEXCEPT
+{
+  return string_literal<CharT, 4>(x[0], x[1], y[0]);
+}
+
+template <class CharT1, class CharT2, std::size_t N1, std::size_t N2>
+CONSTCD14
+inline
+string_literal<typename std::conditional<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>::type,
+               N1 + N2 - 1>
+operator+(const string_literal<CharT1, N1>& x, const string_literal<CharT2, N2>& y) NOEXCEPT
+{
+    using CT = typename std::conditional<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>::type;
+
+    string_literal<CT, N1 + N2 - 1> r;
+    std::size_t i = 0;
+    for (; i < N1-1; ++i)
+       r.p_[i] = CT(x.p_[i]);
+    for (std::size_t j = 0; j < N2; ++j, ++i)
+       r.p_[i] = CT(y.p_[j]);
+
+    return r;
+}
+
+
+template <class CharT, class Traits, class Alloc, std::size_t N>
+inline
+std::basic_string<CharT, Traits, Alloc>
+operator+(std::basic_string<CharT, Traits, Alloc> x, const string_literal<CharT, N>& y)
+{
+    x.append(y.data(), y.size());
+    return x;
+}
+
+#if __cplusplus >= 201402  && (!defined(__EDG_VERSION__) || __EDG_VERSION__ > 411) \
+                           && (!defined(__SUNPRO_CC) || __SUNPRO_CC > 0x5150)
+
+template <class CharT,
+          class = std::enable_if_t<std::is_same<CharT, char>::value ||
+                                   std::is_same<CharT, wchar_t>::value ||
+                                   std::is_same<CharT, char16_t>::value ||
+                                   std::is_same<CharT, char32_t>::value>>
+CONSTCD14
+inline
+string_literal<CharT, 2>
+msl(CharT c) NOEXCEPT
+{
+    return string_literal<CharT, 2>{c};
+}
+
+CONSTCD14
+inline
+std::size_t
+to_string_len(std::intmax_t i)
+{
+    std::size_t r = 0;
+    do
+    {
+        i /= 10;
+        ++r;
+    } while (i > 0);
+    return r;
+}
+
+template <std::intmax_t N>
+CONSTCD14
+inline
+std::enable_if_t
+<
+    N < 10,
+    string_literal<char, to_string_len(N)+1>
+>
+msl() NOEXCEPT
+{
+    return msl(char(N % 10 + '0'));
+}
+
+template <std::intmax_t N>
+CONSTCD14
+inline
+std::enable_if_t
+<
+    10 <= N,
+    string_literal<char, to_string_len(N)+1>
+>
+msl() NOEXCEPT
+{
+    return msl<N/10>() + msl(char(N % 10 + '0'));
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+CONSTCD14
+inline
+std::enable_if_t
+<
+    std::ratio<N, D>::type::den != 1,
+    string_literal<CharT, to_string_len(std::ratio<N, D>::type::num) +
+                          to_string_len(std::ratio<N, D>::type::den) + 4>
+>
+msl(std::ratio<N, D>) NOEXCEPT
+{
+    using R = typename std::ratio<N, D>::type;
+    return msl(CharT{'['}) + msl<R::num>() + msl(CharT{'/'}) +
+                             msl<R::den>() + msl(CharT{']'});
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+CONSTCD14
+inline
+std::enable_if_t
+<
+    std::ratio<N, D>::type::den == 1,
+    string_literal<CharT, to_string_len(std::ratio<N, D>::type::num) + 3>
+>
+msl(std::ratio<N, D>) NOEXCEPT
+{
+    using R = typename std::ratio<N, D>::type;
+    return msl(CharT{'['}) + msl<R::num>() + msl(CharT{']'});
+}
+
+
+#else  // __cplusplus < 201402 || (defined(__EDG_VERSION__) && __EDG_VERSION__ <= 411)
+
+inline
+std::string
+to_string(std::uint64_t x)
+{
+    return std::to_string(x);
+}
+
+template <class CharT>
+inline
+std::basic_string<CharT>
+to_string(std::uint64_t x)
+{
+    auto y = std::to_string(x);
+    return std::basic_string<CharT>(y.begin(), y.end());
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+inline
+typename std::enable_if
+<
+    std::ratio<N, D>::type::den != 1,
+    std::basic_string<CharT>
+>::type
+msl(std::ratio<N, D>)
+{
+    using R = typename std::ratio<N, D>::type;
+    return std::basic_string<CharT>(1, '[') + to_string<CharT>(R::num) + CharT{'/'} +
+                                              to_string<CharT>(R::den) + CharT{']'};
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+inline
+typename std::enable_if
+<
+    std::ratio<N, D>::type::den == 1,
+    std::basic_string<CharT>
+>::type
+msl(std::ratio<N, D>)
+{
+    using R = typename std::ratio<N, D>::type;
+    return std::basic_string<CharT>(1, '[') + to_string<CharT>(R::num) + CharT{']'};
+}
+
+#endif  // __cplusplus < 201402 || (defined(__EDG_VERSION__) && __EDG_VERSION__ <= 411)
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::atto) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'a'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::femto) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'f'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::pico) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'p'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::nano) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'n'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    std::is_same<CharT, char>::value,
+    string_literal<char, 3>
+>::type
+msl(std::micro) NOEXCEPT
+{
+    return string_literal<char, 3>{'\xC2', '\xB5'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    !std::is_same<CharT, char>::value,
+    string_literal<CharT, 2>
+>::type
+msl(std::micro) NOEXCEPT
+{
+    return string_literal<CharT, 2>{CharT{static_cast<unsigned char>('\xB5')}};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::milli) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'m'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::centi) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'c'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 3>
+msl(std::deca) NOEXCEPT
+{
+    return string_literal<CharT, 3>{'d', 'a'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::deci) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'d'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::hecto) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'h'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::kilo) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'k'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::mega) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'M'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::giga) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'G'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::tera) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'T'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::peta) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'P'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::exa) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'E'};
+}
+
+template <class CharT, class Period>
+CONSTCD11
+inline
+auto
+get_units(Period p)
+ -> decltype(msl<CharT>(p) + string_literal<CharT, 2>{'s'})
+{
+    return msl<CharT>(p) + string_literal<CharT, 2>{'s'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+get_units(std::ratio<1>)
+{
+    return string_literal<CharT, 2>{'s'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+get_units(std::ratio<3600>)
+{
+    return string_literal<CharT, 2>{'h'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 4>
+get_units(std::ratio<60>)
+{
+    return string_literal<CharT, 4>{'m', 'i', 'n'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+get_units(std::ratio<86400>)
+{
+    return string_literal<CharT, 2>{'d'};
+}
+
+template <class CharT, class Traits = std::char_traits<CharT>>
+struct make_string;
+
+template <>
+struct make_string<char>
+{
+    template <class Rep>
+    static
+    std::string
+    from(Rep n)
+    {
+        return std::to_string(n);
+    }
+};
+
+template <class Traits>
+struct make_string<char, Traits>
+{
+    template <class Rep>
+    static
+    std::basic_string<char, Traits>
+    from(Rep n)
+    {
+        auto s = std::to_string(n);
+        return std::basic_string<char, Traits>(s.begin(), s.end());
+    }
+};
+
+template <>
+struct make_string<wchar_t>
+{
+    template <class Rep>
+    static
+    std::wstring
+    from(Rep n)
+    {
+        return std::to_wstring(n);
+    }
+};
+
+template <class Traits>
+struct make_string<wchar_t, Traits>
+{
+    template <class Rep>
+    static
+    std::basic_string<wchar_t, Traits>
+    from(Rep n)
+    {
+        auto s = std::to_wstring(n);
+        return std::basic_string<wchar_t, Traits>(s.begin(), s.end());
+    }
+};
+
+}  // namespace detail
+
+// to_stream
+
+CONSTDATA year nanyear{-32768};
+
+template <class Duration>
+struct fields
+{
+    year_month_day        ymd{nanyear/0/0};
+    weekday               wd{8u};
+    hh_mm_ss<Duration>    tod{};
+    bool                  has_tod = false;
+
+#if !defined(__clang__) && defined(__GNUC__) && (__GNUC__ * 100 + __GNUC_MINOR__ <= 409)
+    fields() : ymd{nanyear/0/0}, wd{8u}, tod{}, has_tod{false} {}
+#else
+    fields() = default;
+#endif
+
+    fields(year_month_day ymd_) : ymd(ymd_) {}
+    fields(weekday wd_) : wd(wd_) {}
+    fields(hh_mm_ss<Duration> tod_) : tod(tod_), has_tod(true) {}
+
+    fields(year_month_day ymd_, weekday wd_) : ymd(ymd_), wd(wd_) {}
+    fields(year_month_day ymd_, hh_mm_ss<Duration> tod_) : ymd(ymd_), tod(tod_),
+                                                           has_tod(true) {}
+
+    fields(weekday wd_, hh_mm_ss<Duration> tod_) : wd(wd_), tod(tod_), has_tod(true) {}
+
+    fields(year_month_day ymd_, weekday wd_, hh_mm_ss<Duration> tod_)
+        : ymd(ymd_)
+        , wd(wd_)
+        , tod(tod_)
+        , has_tod(true)
+        {}
+};
+
+namespace detail
+{
+
+template <class CharT, class Traits, class Duration>
+unsigned
+extract_weekday(std::basic_ostream<CharT, Traits>& os, const fields<Duration>& fds)
+{
+    if (!fds.ymd.ok() && !fds.wd.ok())
+    {
+        // fds does not contain a valid weekday
+        os.setstate(std::ios::failbit);
+        return 8;
+    }
+    weekday wd;
+    if (fds.ymd.ok())
+    {
+        wd = weekday{sys_days(fds.ymd)};
+        if (fds.wd.ok() && wd != fds.wd)
+        {
+            // fds.ymd and fds.wd are inconsistent
+            os.setstate(std::ios::failbit);
+            return 8;
+        }
+    }
+    else
+        wd = fds.wd;
+    return static_cast<unsigned>((wd - Sunday).count());
+}
+
+template <class CharT, class Traits, class Duration>
+unsigned
+extract_month(std::basic_ostream<CharT, Traits>& os, const fields<Duration>& fds)
+{
+    if (!fds.ymd.month().ok())
+    {
+        // fds does not contain a valid month
+        os.setstate(std::ios::failbit);
+        return 0;
+    }
+    return static_cast<unsigned>(fds.ymd.month());
+}
+
+}  // namespace detail
+
+#if ONLY_C_LOCALE
+
+namespace detail
+{
+
+inline
+std::pair<const std::string*, const std::string*>
+weekday_names()
+{
+    static const std::string nm[] =
+    {
+        "Sunday",
+        "Monday",
+        "Tuesday",
+        "Wednesday",
+        "Thursday",
+        "Friday",
+        "Saturday",
+        "Sun",
+        "Mon",
+        "Tue",
+        "Wed",
+        "Thu",
+        "Fri",
+        "Sat"
+    };
+    return std::make_pair(nm, nm+sizeof(nm)/sizeof(nm[0]));
+}
+
+inline
+std::pair<const std::string*, const std::string*>
+month_names()
+{
+    static const std::string nm[] =
+    {
+        "January",
+        "February",
+        "March",
+        "April",
+        "May",
+        "June",
+        "July",
+        "August",
+        "September",
+        "October",
+        "November",
+        "December",
+        "Jan",
+        "Feb",
+        "Mar",
+        "Apr",
+        "May",
+        "Jun",
+        "Jul",
+        "Aug",
+        "Sep",
+        "Oct",
+        "Nov",
+        "Dec"
+    };
+    return std::make_pair(nm, nm+sizeof(nm)/sizeof(nm[0]));
+}
+
+inline
+std::pair<const std::string*, const std::string*>
+ampm_names()
+{
+    static const std::string nm[] =
+    {
+        "AM",
+        "PM"
+    };
+    return std::make_pair(nm, nm+sizeof(nm)/sizeof(nm[0]));
+}
+
+template <class CharT, class Traits, class FwdIter>
+FwdIter
+scan_keyword(std::basic_istream<CharT, Traits>& is, FwdIter kb, FwdIter ke)
+{
+    size_t nkw = static_cast<size_t>(std::distance(kb, ke));
+    const unsigned char doesnt_match = '\0';
+    const unsigned char might_match = '\1';
+    const unsigned char does_match = '\2';
+    unsigned char statbuf[100];
+    unsigned char* status = statbuf;
+    std::unique_ptr<unsigned char, void(*)(void*)> stat_hold(0, free);
+    if (nkw > sizeof(statbuf))
+    {
+        status = (unsigned char*)std::malloc(nkw);
+        if (status == nullptr)
+            std::terminate();
+        stat_hold.reset(status);
+    }
+    size_t n_might_match = nkw;  // At this point, any keyword might match
+    size_t n_does_match = 0;     // but none of them definitely do
+    // Initialize all statuses to might_match, except for "" keywords are does_match
+    unsigned char* st = status;
+    for (auto ky = kb; ky != ke; ++ky, ++st)
+    {
+        if (!ky->empty())
+            *st = might_match;
+        else
+        {
+            *st = does_match;
+            --n_might_match;
+            ++n_does_match;
+        }
+    }
+    // While there might be a match, test keywords against the next CharT
+    for (size_t indx = 0; is && n_might_match > 0; ++indx)
+    {
+        // Peek at the next CharT but don't consume it
+        auto ic = is.peek();
+        if (ic == EOF)
+        {
+            is.setstate(std::ios::eofbit);
+            break;
+        }
+        auto c = static_cast<char>(toupper(static_cast<unsigned char>(ic)));
+        bool consume = false;
+        // For each keyword which might match, see if the indx character is c
+        // If a match if found, consume c
+        // If a match is found, and that is the last character in the keyword,
+        //    then that keyword matches.
+        // If the keyword doesn't match this character, then change the keyword
+        //    to doesn't match
+        st = status;
+        for (auto ky = kb; ky != ke; ++ky, ++st)
+        {
+            if (*st == might_match)
+            {
+                if (c == static_cast<char>(toupper(static_cast<unsigned char>((*ky)[indx]))))
+                {
+                    consume = true;
+                    if (ky->size() == indx+1)
+                    {
+                        *st = does_match;
+                        --n_might_match;
+                        ++n_does_match;
+                    }
+                }
+                else
+                {
+                    *st = doesnt_match;
+                    --n_might_match;
+                }
+            }
+        }
+        // consume if we matched a character
+        if (consume)
+        {
+            (void)is.get();
+            // If we consumed a character and there might be a matched keyword that
+            //   was marked matched on a previous iteration, then such keywords
+            //   are now marked as not matching.
+            if (n_might_match + n_does_match > 1)
+            {
+                st = status;
+                for (auto ky = kb; ky != ke; ++ky, ++st)
+                {
+                    if (*st == does_match && ky->size() != indx+1)
+                    {
+                        *st = doesnt_match;
+                        --n_does_match;
+                    }
+                }
+            }
+        }
+    }
+    // We've exited the loop because we hit eof and/or we have no more "might matches".
+    // Return the first matching result
+    for (st = status; kb != ke; ++kb, ++st)
+        if (*st == does_match)
+            break;
+    if (kb == ke)
+        is.setstate(std::ios::failbit);
+    return kb;
+}
+
+}  // namespace detail
+
+#endif  // ONLY_C_LOCALE
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const fields<Duration>& fds, const std::string* abbrev,
+          const std::chrono::seconds* offset_sec)
+{
+#if ONLY_C_LOCALE
+    using detail::weekday_names;
+    using detail::month_names;
+    using detail::ampm_names;
+#endif
+    using detail::save_ostream;
+    using detail::get_units;
+    using detail::extract_weekday;
+    using detail::extract_month;
+    using std::ios;
+    using std::chrono::duration_cast;
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    using std::chrono::hours;
+    date::detail::save_ostream<CharT, Traits> ss(os);
+    os.fill(' ');
+    os.flags(std::ios::skipws | std::ios::dec);
+    os.width(0);
+    tm tm{};
+    bool insert_negative = fds.has_tod && fds.tod.to_duration() < Duration::zero();
+#if !ONLY_C_LOCALE
+    auto& facet = std::use_facet<std::time_put<CharT>>(os.getloc());
+#endif
+    const CharT* command = nullptr;
+    CharT modified = CharT{};
+    for (; *fmt; ++fmt)
+    {
+        switch (*fmt)
+        {
+        case 'a':
+        case 'A':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                    if (os.fail())
+                        return os;
+#if !ONLY_C_LOCALE
+                    const CharT f[] = {'%', *fmt};
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+#else  // ONLY_C_LOCALE
+                    os << weekday_names().first[tm.tm_wday+7*(*fmt == 'a')];
+#endif  // ONLY_C_LOCALE
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'b':
+        case 'B':
+        case 'h':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    tm.tm_mon = static_cast<int>(extract_month(os, fds)) - 1;
+#if !ONLY_C_LOCALE
+                    const CharT f[] = {'%', *fmt};
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+#else  // ONLY_C_LOCALE
+                    os << month_names().first[tm.tm_mon+12*(*fmt != 'B')];
+#endif  // ONLY_C_LOCALE
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'c':
+        case 'x':
+            if (command)
+            {
+                if (modified == CharT{'O'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    if (*fmt == 'c' && !fds.has_tod)
+                        os.setstate(std::ios::failbit);
+#if !ONLY_C_LOCALE
+                    tm = std::tm{};
+                    auto const& ymd = fds.ymd;
+                    auto ld = local_days(ymd);
+                    if (*fmt == 'c')
+                    {
+                        tm.tm_sec = static_cast<int>(fds.tod.seconds().count());
+                        tm.tm_min = static_cast<int>(fds.tod.minutes().count());
+                        tm.tm_hour = static_cast<int>(fds.tod.hours().count());
+                    }
+                    tm.tm_mday = static_cast<int>(static_cast<unsigned>(ymd.day()));
+                    tm.tm_mon = static_cast<int>(extract_month(os, fds) - 1);
+                    tm.tm_year = static_cast<int>(ymd.year()) - 1900;
+                    tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                    if (os.fail())
+                        return os;
+                    tm.tm_yday = static_cast<int>((ld - local_days(ymd.year()/1/1)).count());
+                    CharT f[3] = {'%'};
+                    auto fe = std::begin(f) + 1;
+                    if (modified == CharT{'E'})
+                        *fe++ = modified;
+                    *fe++ = *fmt;
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), fe);
+#else  // ONLY_C_LOCALE
+                    if (*fmt == 'c')
+                    {
+                        auto wd = static_cast<int>(extract_weekday(os, fds));
+                        os << weekday_names().first[static_cast<unsigned>(wd)+7]
+                           << ' ';
+                        os << month_names().first[extract_month(os, fds)-1+12] << ' ';
+                        auto d = static_cast<int>(static_cast<unsigned>(fds.ymd.day()));
+                        if (d < 10)
+                            os << ' ';
+                        os << d << ' '
+                           << make_time(duration_cast<seconds>(fds.tod.to_duration()))
+                           << ' ' << fds.ymd.year();
+
+                    }
+                    else  // *fmt == 'x'
+                    {
+                        auto const& ymd = fds.ymd;
+                        save_ostream<CharT, Traits> _(os);
+                        os.fill('0');
+                        os.flags(std::ios::dec | std::ios::right);
+                        os.width(2);
+                        os << static_cast<unsigned>(ymd.month()) << CharT{'/'};
+                        os.width(2);
+                        os << static_cast<unsigned>(ymd.day()) << CharT{'/'};
+                        os.width(2);
+                        os << static_cast<int>(ymd.year()) % 100;
+                    }
+#endif  // ONLY_C_LOCALE
+                }
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'C':
+            if (command)
+            {
+                if (modified == CharT{'O'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.year().ok())
+                        os.setstate(std::ios::failbit);
+                    auto y = static_cast<int>(fds.ymd.year());
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        save_ostream<CharT, Traits> _(os);
+                        os.fill('0');
+                        os.flags(std::ios::dec | std::ios::right);
+                        if (y >= 0)
+                        {
+                            os.width(2);
+                            os << y/100;
+                        }
+                        else
+                        {
+                            os << CharT{'-'};
+                            os.width(2);
+                            os << -(y-99)/100;
+                        }
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'E'})
+                    {
+                        tm.tm_year = y - 1900;
+                        CharT f[3] = {'%', 'E', 'C'};
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'd':
+        case 'e':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.day().ok())
+                        os.setstate(std::ios::failbit);
+                    auto d = static_cast<int>(static_cast<unsigned>(fds.ymd.day()));
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        save_ostream<CharT, Traits> _(os);
+                        if (*fmt == CharT{'d'})
+                            os.fill('0');
+                        else
+                            os.fill(' ');
+                        os.flags(std::ios::dec | std::ios::right);
+                        os.width(2);
+                        os << d;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        tm.tm_mday = d;
+                        CharT f[3] = {'%', 'O', *fmt};
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'D':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto const& ymd = fds.ymd;
+                    save_ostream<CharT, Traits> _(os);
+                    os.fill('0');
+                    os.flags(std::ios::dec | std::ios::right);
+                    os.width(2);
+                    os << static_cast<unsigned>(ymd.month()) << CharT{'/'};
+                    os.width(2);
+                    os << static_cast<unsigned>(ymd.day()) << CharT{'/'};
+                    os.width(2);
+                    os << static_cast<int>(ymd.year()) % 100;
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'F':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto const& ymd = fds.ymd;
+                    save_ostream<CharT, Traits> _(os);
+                    os.imbue(std::locale::classic());
+                    os.fill('0');
+                    os.flags(std::ios::dec | std::ios::right);
+                    os.width(4);
+                    os << static_cast<int>(ymd.year()) << CharT{'-'};
+                    os.width(2);
+                    os << static_cast<unsigned>(ymd.month()) << CharT{'-'};
+                    os.width(2);
+                    os << static_cast<unsigned>(ymd.day());
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'g':
+        case 'G':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto ld = local_days(fds.ymd);
+                    auto y = year_month_day{ld + days{3}}.year();
+                    auto start = local_days((y-years{1})/December/Thursday[last]) +
+                                 (Monday-Thursday);
+                    if (ld < start)
+                        --y;
+                    if (*fmt == CharT{'G'})
+                        os << y;
+                    else
+                    {
+                        save_ostream<CharT, Traits> _(os);
+                        os.fill('0');
+                        os.flags(std::ios::dec | std::ios::right);
+                        os.width(2);
+                        os << std::abs(static_cast<int>(y)) % 100;
+                    }
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'H':
+        case 'I':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    if (insert_negative)
+                    {
+                        os << '-';
+                        insert_negative = false;
+                    }
+                    auto hms = fds.tod;
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        auto h = *fmt == CharT{'I'} ? date::make12(hms.hours()) : hms.hours();
+                        if (h < hours{10})
+                            os << CharT{'0'};
+                        os << h.count();
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_hour = static_cast<int>(hms.hours().count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'j':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (fds.ymd.ok() || fds.has_tod)
+                    {
+                        days doy;
+                        if (fds.ymd.ok())
+                        {
+                            auto ld = local_days(fds.ymd);
+                            auto y = fds.ymd.year();
+                            doy = ld - local_days(y/January/1) + days{1};
+                        }
+                        else
+                        {
+                            doy = duration_cast<days>(fds.tod.to_duration());
+                        }
+                        save_ostream<CharT, Traits> _(os);
+                        os.fill('0');
+                        os.flags(std::ios::dec | std::ios::right);
+                        os.width(3);
+                        os << doy.count();
+                    }
+                    else
+                    {
+                        os.setstate(std::ios::failbit);
+                    }
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'm':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.month().ok())
+                        os.setstate(std::ios::failbit);
+                    auto m = static_cast<unsigned>(fds.ymd.month());
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        if (m < 10)
+                            os << CharT{'0'};
+                        os << m;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_mon = static_cast<int>(m-1);
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'M':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    if (insert_negative)
+                    {
+                        os << '-';
+                        insert_negative = false;
+                    }
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        if (fds.tod.minutes() < minutes{10})
+                            os << CharT{'0'};
+                        os << fds.tod.minutes().count();
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_min = static_cast<int>(fds.tod.minutes().count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'n':
+            if (command)
+            {
+                if (modified == CharT{})
+                    os << CharT{'\n'};
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'p':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+#if !ONLY_C_LOCALE
+                    const CharT f[] = {'%', *fmt};
+                    tm.tm_hour = static_cast<int>(fds.tod.hours().count());
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+#else
+                    if (date::is_am(fds.tod.hours()))
+                        os << ampm_names().first[0];
+                    else
+                        os << ampm_names().first[1];
+#endif
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'Q':
+        case 'q':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    auto d = fds.tod.to_duration();
+                    if (*fmt == 'q')
+                        os << get_units<CharT>(typename decltype(d)::period::type{});
+                    else
+                        os << d.count();
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'r':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+#if !ONLY_C_LOCALE
+                    const CharT f[] = {'%', *fmt};
+                    tm.tm_hour = static_cast<int>(fds.tod.hours().count());
+                    tm.tm_min = static_cast<int>(fds.tod.minutes().count());
+                    tm.tm_sec = static_cast<int>(fds.tod.seconds().count());
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+#else
+                    hh_mm_ss<seconds> tod(duration_cast<seconds>(fds.tod.to_duration()));
+                    save_ostream<CharT, Traits> _(os);
+                    os.fill('0');
+                    os.width(2);
+                    os << date::make12(tod.hours()).count() << CharT{':'};
+                    os.width(2);
+                    os << tod.minutes().count() << CharT{':'};
+                    os.width(2);
+                    os << tod.seconds().count() << CharT{' '};
+                    if (date::is_am(tod.hours()))
+                        os << ampm_names().first[0];
+                    else
+                        os << ampm_names().first[1];
+#endif
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'R':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    if (fds.tod.hours() < hours{10})
+                        os << CharT{'0'};
+                    os << fds.tod.hours().count() << CharT{':'};
+                    if (fds.tod.minutes() < minutes{10})
+                        os << CharT{'0'};
+                    os << fds.tod.minutes().count();
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'S':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    if (insert_negative)
+                    {
+                        os << '-';
+                        insert_negative = false;
+                    }
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        os << fds.tod.s_;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_sec = static_cast<int>(fds.tod.s_.seconds().count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 't':
+            if (command)
+            {
+                if (modified == CharT{})
+                    os << CharT{'\t'};
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'T':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    os << fds.tod;
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'u':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    auto wd = extract_weekday(os, fds);
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        os << (wd != 0 ? wd : 7u);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_wday = static_cast<int>(wd);
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'U':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    auto const& ymd = fds.ymd;
+                    if (!ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto ld = local_days(ymd);
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        auto st = local_days(Sunday[1]/January/ymd.year());
+                        if (ld < st)
+                            os << CharT{'0'} << CharT{'0'};
+                        else
+                        {
+                            auto wn = duration_cast<weeks>(ld - st).count() + 1;
+                            if (wn < 10)
+                                os << CharT{'0'};
+                            os << wn;
+                        }
+                   }
+ #if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_year = static_cast<int>(ymd.year()) - 1900;
+                        tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                        if (os.fail())
+                            return os;
+                        tm.tm_yday = static_cast<int>((ld - local_days(ymd.year()/1/1)).count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'V':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto ld = local_days(fds.ymd);
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        auto y = year_month_day{ld + days{3}}.year();
+                        auto st = local_days((y-years{1})/12/Thursday[last]) +
+                                  (Monday-Thursday);
+                        if (ld < st)
+                        {
+                            --y;
+                            st = local_days((y - years{1})/12/Thursday[last]) +
+                                 (Monday-Thursday);
+                        }
+                        auto wn = duration_cast<weeks>(ld - st).count() + 1;
+                        if (wn < 10)
+                            os << CharT{'0'};
+                        os << wn;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        auto const& ymd = fds.ymd;
+                        tm.tm_year = static_cast<int>(ymd.year()) - 1900;
+                        tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                        if (os.fail())
+                            return os;
+                        tm.tm_yday = static_cast<int>((ld - local_days(ymd.year()/1/1)).count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'w':
+            if (command)
+            {
+                auto wd = extract_weekday(os, fds);
+                if (os.fail())
+                    return os;
+#if !ONLY_C_LOCALE
+                if (modified == CharT{})
+#else
+                if (modified != CharT{'E'})
+#endif
+                {
+                    os << wd;
+                }
+#if !ONLY_C_LOCALE
+                else if (modified == CharT{'O'})
+                {
+                    const CharT f[] = {'%', modified, *fmt};
+                    tm.tm_wday = static_cast<int>(wd);
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                }
+#endif
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'W':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    auto const& ymd = fds.ymd;
+                    if (!ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto ld = local_days(ymd);
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        auto st = local_days(Monday[1]/January/ymd.year());
+                        if (ld < st)
+                            os << CharT{'0'} << CharT{'0'};
+                        else
+                        {
+                            auto wn = duration_cast<weeks>(ld - st).count() + 1;
+                            if (wn < 10)
+                                os << CharT{'0'};
+                            os << wn;
+                        }
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_year = static_cast<int>(ymd.year()) - 1900;
+                        tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                        if (os.fail())
+                            return os;
+                        tm.tm_yday = static_cast<int>((ld - local_days(ymd.year()/1/1)).count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'X':
+            if (command)
+            {
+                if (modified == CharT{'O'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+#if !ONLY_C_LOCALE
+                    tm = std::tm{};
+                    tm.tm_sec = static_cast<int>(fds.tod.seconds().count());
+                    tm.tm_min = static_cast<int>(fds.tod.minutes().count());
+                    tm.tm_hour = static_cast<int>(fds.tod.hours().count());
+                    CharT f[3] = {'%'};
+                    auto fe = std::begin(f) + 1;
+                    if (modified == CharT{'E'})
+                        *fe++ = modified;
+                    *fe++ = *fmt;
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), fe);
+#else
+                    os << fds.tod;
+#endif
+                }
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'y':
+            if (command)
+            {
+                if (!fds.ymd.year().ok())
+                    os.setstate(std::ios::failbit);
+                auto y = static_cast<int>(fds.ymd.year());
+#if !ONLY_C_LOCALE
+                if (modified == CharT{})
+                {
+#endif
+                    y = std::abs(y) % 100;
+                    if (y < 10)
+                        os << CharT{'0'};
+                    os << y;
+#if !ONLY_C_LOCALE
+                }
+                else
+                {
+                    const CharT f[] = {'%', modified, *fmt};
+                    tm.tm_year = y - 1900;
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                }
+#endif
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'Y':
+            if (command)
+            {
+                if (modified == CharT{'O'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.year().ok())
+                        os.setstate(std::ios::failbit);
+                    auto y = fds.ymd.year();
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        save_ostream<CharT, Traits> _(os);
+                        os.imbue(std::locale::classic());
+                        os << y;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'E'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_year = static_cast<int>(y) - 1900;
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'z':
+            if (command)
+            {
+                if (offset_sec == nullptr)
+                {
+                    // Can not format %z with unknown offset
+                    os.setstate(ios::failbit);
+                    return os;
+                }
+                auto m = duration_cast<minutes>(*offset_sec);
+                auto neg = m < minutes{0};
+                m = date::abs(m);
+                auto h = duration_cast<hours>(m);
+                m -= h;
+                if (neg)
+                    os << CharT{'-'};
+                else
+                    os << CharT{'+'};
+                if (h < hours{10})
+                    os << CharT{'0'};
+                os << h.count();
+                if (modified != CharT{})
+                    os << CharT{':'};
+                if (m < minutes{10})
+                    os << CharT{'0'};
+                os << m.count();
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'Z':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (abbrev == nullptr)
+                    {
+                        // Can not format %Z with unknown time_zone
+                        os.setstate(ios::failbit);
+                        return os;
+                    }
+                    for (auto c : *abbrev)
+                        os << CharT(c);
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'E':
+        case 'O':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    modified = *fmt;
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    command = nullptr;
+                    modified = CharT{};
+                }
+            }
+            else
+                os << *fmt;
+            break;
+        case '%':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    os << CharT{'%'};
+                    command = nullptr;
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << CharT{'%'};
+                    command = nullptr;
+                    modified = CharT{};
+                }
+            }
+            else
+                command = fmt;
+            break;
+        default:
+            if (command)
+            {
+                os << CharT{'%'};
+                command = nullptr;
+            }
+            if (modified != CharT{})
+            {
+                os << modified;
+                modified = CharT{};
+            }
+            os << *fmt;
+            break;
+        }
+    }
+    if (command)
+        os << CharT{'%'};
+    if (modified != CharT{})
+        os << modified;
+    return os;
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const year& y)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{y/0/0};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const month& m)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{m/0/nanyear};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const day& d)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{d/0/nanyear};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const weekday& wd)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{wd};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const year_month& ym)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{ym/0};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const month_day& md)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{md/nanyear};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const year_month_day& ymd)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{ymd};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits, class Rep, class Period>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const std::chrono::duration<Rep, Period>& d)
+{
+    using Duration = std::chrono::duration<Rep, Period>;
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    fields<CT> fds{hh_mm_ss<CT>{d}};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const local_time<Duration>& tp, const std::string* abbrev = nullptr,
+          const std::chrono::seconds* offset_sec = nullptr)
+{
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    auto ld = std::chrono::time_point_cast<days>(tp);
+    fields<CT> fds;
+    if (ld <= tp)
+        fds = fields<CT>{year_month_day{ld}, hh_mm_ss<CT>{tp-local_seconds{ld}}};
+    else
+        fds = fields<CT>{year_month_day{ld - days{1}},
+                         hh_mm_ss<CT>{days{1} - (local_seconds{ld} - tp)}};
+    return to_stream(os, fmt, fds, abbrev, offset_sec);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const sys_time<Duration>& tp)
+{
+    using std::chrono::seconds;
+    using CT = typename std::common_type<Duration, seconds>::type;
+    const std::string abbrev("UTC");
+    CONSTDATA seconds offset{0};
+    auto sd = std::chrono::time_point_cast<days>(tp);
+    fields<CT> fds;
+    if (sd <= tp)
+        fds = fields<CT>{year_month_day{sd}, hh_mm_ss<CT>{tp-sys_seconds{sd}}};
+    else
+        fds = fields<CT>{year_month_day{sd - days{1}},
+                         hh_mm_ss<CT>{days{1} - (sys_seconds{sd} - tp)}};
+    return to_stream(os, fmt, fds, &abbrev, &offset);
+}
+
+// format
+
+template <class CharT, class Streamable>
+auto
+format(const std::locale& loc, const CharT* fmt, const Streamable& tp)
+    -> decltype(to_stream(std::declval<std::basic_ostream<CharT>&>(), fmt, tp),
+                std::basic_string<CharT>{})
+{
+    std::basic_ostringstream<CharT> os;
+    os.exceptions(std::ios::failbit | std::ios::badbit);
+    os.imbue(loc);
+    to_stream(os, fmt, tp);
+    return os.str();
+}
+
+template <class CharT, class Streamable>
+auto
+format(const CharT* fmt, const Streamable& tp)
+    -> decltype(to_stream(std::declval<std::basic_ostream<CharT>&>(), fmt, tp),
+                std::basic_string<CharT>{})
+{
+    std::basic_ostringstream<CharT> os;
+    os.exceptions(std::ios::failbit | std::ios::badbit);
+    to_stream(os, fmt, tp);
+    return os.str();
+}
+
+template <class CharT, class Traits, class Alloc, class Streamable>
+auto
+format(const std::locale& loc, const std::basic_string<CharT, Traits, Alloc>& fmt,
+       const Streamable& tp)
+    -> decltype(to_stream(std::declval<std::basic_ostream<CharT, Traits>&>(), fmt.c_str(), tp),
+                std::basic_string<CharT, Traits, Alloc>{})
+{
+    std::basic_ostringstream<CharT, Traits, Alloc> os;
+    os.exceptions(std::ios::failbit | std::ios::badbit);
+    os.imbue(loc);
+    to_stream(os, fmt.c_str(), tp);
+    return os.str();
+}
+
+template <class CharT, class Traits, class Alloc, class Streamable>
+auto
+format(const std::basic_string<CharT, Traits, Alloc>& fmt, const Streamable& tp)
+    -> decltype(to_stream(std::declval<std::basic_ostream<CharT, Traits>&>(), fmt.c_str(), tp),
+                std::basic_string<CharT, Traits, Alloc>{})
+{
+    std::basic_ostringstream<CharT, Traits, Alloc> os;
+    os.exceptions(std::ios::failbit | std::ios::badbit);
+    to_stream(os, fmt.c_str(), tp);
+    return os.str();
+}
+
+// parse
+
+namespace detail
+{
+
+template <class CharT, class Traits>
+bool
+read_char(std::basic_istream<CharT, Traits>& is, CharT fmt, std::ios::iostate& err)
+{
+    auto ic = is.get();
+    if (Traits::eq_int_type(ic, Traits::eof()) ||
+       !Traits::eq(Traits::to_char_type(ic), fmt))
+    {
+        err |= std::ios::failbit;
+        is.setstate(std::ios::failbit);
+        return false;
+    }
+    return true;
+}
+
+template <class CharT, class Traits>
+unsigned
+read_unsigned(std::basic_istream<CharT, Traits>& is, unsigned m = 1, unsigned M = 10)
+{
+    unsigned x = 0;
+    unsigned count = 0;
+    while (true)
+    {
+        auto ic = is.peek();
+        if (Traits::eq_int_type(ic, Traits::eof()))
+            break;
+        auto c = static_cast<char>(Traits::to_char_type(ic));
+        if (!('0' <= c && c <= '9'))
+            break;
+        (void)is.get();
+        ++count;
+        x = 10*x + static_cast<unsigned>(c - '0');
+        if (count == M)
+            break;
+    }
+    if (count < m)
+        is.setstate(std::ios::failbit);
+    return x;
+}
+
+template <class CharT, class Traits>
+int
+read_signed(std::basic_istream<CharT, Traits>& is, unsigned m = 1, unsigned M = 10)
+{
+    auto ic = is.peek();
+    if (!Traits::eq_int_type(ic, Traits::eof()))
+    {
+        auto c = static_cast<char>(Traits::to_char_type(ic));
+        if (('0' <= c && c <= '9') || c == '-' || c == '+')
+        {
+            if (c == '-' || c == '+')
+                (void)is.get();
+            auto x = static_cast<int>(read_unsigned(is, std::max(m, 1u), M));
+            if (!is.fail())
+            {
+                if (c == '-')
+                    x = -x;
+                return x;
+            }
+        }
+    }
+    if (m > 0)
+        is.setstate(std::ios::failbit);
+    return 0;
+}
+
+template <class CharT, class Traits>
+long double
+read_long_double(std::basic_istream<CharT, Traits>& is, unsigned m = 1, unsigned M = 10)
+{
+    unsigned count = 0;
+    unsigned fcount = 0;
+    unsigned long long i = 0;
+    unsigned long long f = 0;
+    bool parsing_fraction = false;
+#if ONLY_C_LOCALE
+    typename Traits::int_type decimal_point = '.';
+#else
+    auto decimal_point = Traits::to_int_type(
+        std::use_facet<std::numpunct<CharT>>(is.getloc()).decimal_point());
+#endif
+    while (true)
+    {
+        auto ic = is.peek();
+        if (Traits::eq_int_type(ic, Traits::eof()))
+            break;
+        if (Traits::eq_int_type(ic, decimal_point))
+        {
+            decimal_point = Traits::eof();
+            parsing_fraction = true;
+        }
+        else
+        {
+            auto c = static_cast<char>(Traits::to_char_type(ic));
+            if (!('0' <= c && c <= '9'))
+                break;
+            if (!parsing_fraction)
+            {
+                i = 10*i + static_cast<unsigned>(c - '0');
+            }
+            else
+            {
+                f = 10*f + static_cast<unsigned>(c - '0');
+                ++fcount;
+            }
+        }
+        (void)is.get();
+        if (++count == M)
+            break;
+    }
+    if (count < m)
+    {
+        is.setstate(std::ios::failbit);
+        return 0;
+    }
+    return static_cast<long double>(i) + static_cast<long double>(f)/std::pow(10.L, fcount);
+}
+
+struct rs
+{
+    int& i;
+    unsigned m;
+    unsigned M;
+};
+
+struct ru
+{
+    int& i;
+    unsigned m;
+    unsigned M;
+};
+
+struct rld
+{
+    long double& i;
+    unsigned m;
+    unsigned M;
+};
+
+template <class CharT, class Traits>
+void
+read(std::basic_istream<CharT, Traits>&)
+{
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, CharT a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, rs a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, ru a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, int a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, rld a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, CharT a0, Args&& ...args)
+{
+    // No-op if a0 == CharT{}
+    if (a0 != CharT{})
+    {
+        auto ic = is.peek();
+        if (Traits::eq_int_type(ic, Traits::eof()))
+        {
+            is.setstate(std::ios::failbit | std::ios::eofbit);
+            return;
+        }
+        if (!Traits::eq(Traits::to_char_type(ic), a0))
+        {
+            is.setstate(std::ios::failbit);
+            return;
+        }
+        (void)is.get();
+    }
+    read(is, std::forward<Args>(args)...);
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, rs a0, Args&& ...args)
+{
+    auto x = read_signed(is, a0.m, a0.M);
+    if (is.fail())
+        return;
+    a0.i = x;
+    read(is, std::forward<Args>(args)...);
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, ru a0, Args&& ...args)
+{
+    auto x = read_unsigned(is, a0.m, a0.M);
+    if (is.fail())
+        return;
+    a0.i = static_cast<int>(x);
+    read(is, std::forward<Args>(args)...);
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, int a0, Args&& ...args)
+{
+    if (a0 != -1)
+    {
+        auto u = static_cast<unsigned>(a0);
+        CharT buf[std::numeric_limits<unsigned>::digits10+2u] = {};
+        auto e = buf;
+        do
+        {
+            *e++ = static_cast<CharT>(CharT(u % 10) + CharT{'0'});
+            u /= 10;
+        } while (u > 0);
+        std::reverse(buf, e);
+        for (auto p = buf; p != e && is.rdstate() == std::ios::goodbit; ++p)
+            read(is, *p);
+    }
+    if (is.rdstate() == std::ios::goodbit)
+        read(is, std::forward<Args>(args)...);
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, rld a0, Args&& ...args)
+{
+    auto x = read_long_double(is, a0.m, a0.M);
+    if (is.fail())
+        return;
+    a0.i = x;
+    read(is, std::forward<Args>(args)...);
+}
+
+template <class T, class CharT, class Traits>
+inline
+void
+checked_set(T& value, T from, T not_a_value, std::basic_ios<CharT, Traits>& is)
+{
+    if (!is.fail())
+    {
+        if (value == not_a_value)
+            value = std::move(from);
+        else if (value != from)
+            is.setstate(std::ios::failbit);
+    }
+}
+
+}  // namespace detail;
+
+template <class CharT, class Traits, class Duration, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            fields<Duration>& fds, std::basic_string<CharT, Traits, Alloc>* abbrev,
+            std::chrono::minutes* offset)
+{
+    using std::numeric_limits;
+    using std::ios;
+    using std::chrono::duration;
+    using std::chrono::duration_cast;
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    using std::chrono::hours;
+    using detail::round_i;
+    typename std::basic_istream<CharT, Traits>::sentry ok{is, true};
+    if (ok)
+    {
+        date::detail::save_istream<CharT, Traits> ss(is);
+        is.fill(' ');
+        is.flags(std::ios::skipws | std::ios::dec);
+        is.width(0);
+#if !ONLY_C_LOCALE
+        auto& f = std::use_facet<std::time_get<CharT>>(is.getloc());
+        std::tm tm{};
+#endif
+        const CharT* command = nullptr;
+        auto modified = CharT{};
+        auto width = -1;
+
+        CONSTDATA int not_a_year = numeric_limits<short>::min();
+        CONSTDATA int not_a_2digit_year = 100;
+        CONSTDATA int not_a_century = not_a_year / 100;
+        CONSTDATA int not_a_month = 0;
+        CONSTDATA int not_a_day = 0;
+        CONSTDATA int not_a_hour = numeric_limits<int>::min();
+        CONSTDATA int not_a_hour_12_value = 0;
+        CONSTDATA int not_a_minute = not_a_hour;
+        CONSTDATA Duration not_a_second = Duration::min();
+        CONSTDATA int not_a_doy = -1;
+        CONSTDATA int not_a_weekday = 8;
+        CONSTDATA int not_a_week_num = 100;
+        CONSTDATA int not_a_ampm = -1;
+        CONSTDATA minutes not_a_offset = minutes::min();
+
+        int Y = not_a_year;             // c, F, Y                   *
+        int y = not_a_2digit_year;      // D, x, y                   *
+        int g = not_a_2digit_year;      // g                         *
+        int G = not_a_year;             // G                         *
+        int C = not_a_century;          // C                         *
+        int m = not_a_month;            // b, B, h, m, c, D, F, x    *
+        int d = not_a_day;              // c, d, D, e, F, x          *
+        int j = not_a_doy;              // j                         *
+        int wd = not_a_weekday;         // a, A, u, w                *
+        int H = not_a_hour;             // c, H, R, T, X             *
+        int I = not_a_hour_12_value;    // I, r                      *
+        int p = not_a_ampm;             // p, r                      *
+        int M = not_a_minute;           // c, M, r, R, T, X          *
+        Duration s = not_a_second;      // c, r, S, T, X             *
+        int U = not_a_week_num;         // U                         *
+        int V = not_a_week_num;         // V                         *
+        int W = not_a_week_num;         // W                         *
+        std::basic_string<CharT, Traits, Alloc> temp_abbrev;  // Z   *
+        minutes temp_offset = not_a_offset;  // z                    *
+
+        using detail::read;
+        using detail::rs;
+        using detail::ru;
+        using detail::rld;
+        using detail::checked_set;
+        for (; *fmt != CharT{} && !is.fail(); ++fmt)
+        {
+            switch (*fmt)
+            {
+            case 'a':
+            case 'A':
+            case 'u':
+            case 'w':  // wd:  a, A, u, w
+                if (command)
+                {
+                    int trial_wd = not_a_weekday;
+                    if (*fmt == 'a' || *fmt == 'A')
+                    {
+                        if (modified == CharT{})
+                        {
+#if !ONLY_C_LOCALE
+                            ios::iostate err = ios::goodbit;
+                            f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                            is.setstate(err);
+                            if (!is.fail())
+                                trial_wd = tm.tm_wday;
+#else
+                            auto nm = detail::weekday_names();
+                            auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                            if (!is.fail())
+                                trial_wd = i % 7;
+#endif
+                        }
+                        else
+                            read(is, CharT{'%'}, width, modified, *fmt);
+                    }
+                    else  // *fmt == 'u' || *fmt == 'w'
+                    {
+#if !ONLY_C_LOCALE
+                        if (modified == CharT{})
+#else
+                        if (modified != CharT{'E'})
+#endif
+                        {
+                            read(is, ru{trial_wd, 1, width == -1 ?
+                                                      1u : static_cast<unsigned>(width)});
+                            if (!is.fail())
+                            {
+                                if (*fmt == 'u')
+                                {
+                                    if (!(1 <= trial_wd && trial_wd <= 7))
+                                    {
+                                        trial_wd = not_a_weekday;
+                                        is.setstate(ios::failbit);
+                                    }
+                                    else if (trial_wd == 7)
+                                        trial_wd = 0;
+                                }
+                                else  // *fmt == 'w'
+                                {
+                                    if (!(0 <= trial_wd && trial_wd <= 6))
+                                    {
+                                        trial_wd = not_a_weekday;
+                                        is.setstate(ios::failbit);
+                                    }
+                                }
+                            }
+                        }
+#if !ONLY_C_LOCALE
+                        else if (modified == CharT{'O'})
+                        {
+                            ios::iostate err = ios::goodbit;
+                            f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                            is.setstate(err);
+                            if (!is.fail())
+                                trial_wd = tm.tm_wday;
+                        }
+#endif
+                        else
+                            read(is, CharT{'%'}, width, modified, *fmt);
+                    }
+                    if (trial_wd != not_a_weekday)
+                        checked_set(wd, trial_wd, not_a_weekday, is);
+                }
+                else  // !command
+                    read(is, *fmt);
+                command = nullptr;
+                width = -1;
+                modified = CharT{};
+                break;
+            case 'b':
+            case 'B':
+            case 'h':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int ttm = not_a_month;
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            ttm = tm.tm_mon + 1;
+                        is.setstate(err);
+#else
+                        auto nm = detail::month_names();
+                        auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        if (!is.fail())
+                            ttm = i % 12 + 1;
+#endif
+                        checked_set(m, ttm, not_a_month, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'c':
+                if (command)
+                {
+                    if (modified != CharT{'O'})
+                    {
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            checked_set(Y, tm.tm_year + 1900, not_a_year, is);
+                            checked_set(m, tm.tm_mon + 1, not_a_month, is);
+                            checked_set(d, tm.tm_mday, not_a_day, is);
+                            checked_set(H, tm.tm_hour, not_a_hour, is);
+                            checked_set(M, tm.tm_min, not_a_minute, is);
+                            checked_set(s, duration_cast<Duration>(seconds{tm.tm_sec}),
+                                        not_a_second, is);
+                        }
+                        is.setstate(err);
+#else
+                        // "%a %b %e %T %Y"
+                        auto nm = detail::weekday_names();
+                        auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        checked_set(wd, static_cast<int>(i % 7), not_a_weekday, is);
+                        ws(is);
+                        nm = detail::month_names();
+                        i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        checked_set(m, static_cast<int>(i % 12 + 1), not_a_month, is);
+                        ws(is);
+                        int td = not_a_day;
+                        read(is, rs{td, 1, 2});
+                        checked_set(d, td, not_a_day, is);
+                        ws(is);
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        int tH;
+                        int tM;
+                        long double S{};
+                        read(is, ru{tH, 1, 2}, CharT{':'}, ru{tM, 1, 2},
+                                               CharT{':'}, rld{S, 1, w});
+                        checked_set(H, tH, not_a_hour, is);
+                        checked_set(M, tM, not_a_minute, is);
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+                        ws(is);
+                        int tY = not_a_year;
+                        read(is, rs{tY, 1, 4u});
+                        checked_set(Y, tY, not_a_year, is);
+#endif
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'x':
+                if (command)
+                {
+                    if (modified != CharT{'O'})
+                    {
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            checked_set(Y, tm.tm_year + 1900, not_a_year, is);
+                            checked_set(m, tm.tm_mon + 1, not_a_month, is);
+                            checked_set(d, tm.tm_mday, not_a_day, is);
+                        }
+                        is.setstate(err);
+#else
+                        // "%m/%d/%y"
+                        int ty = not_a_2digit_year;
+                        int tm = not_a_month;
+                        int td = not_a_day;
+                        read(is, ru{tm, 1, 2}, CharT{'/'}, ru{td, 1, 2}, CharT{'/'},
+                                 rs{ty, 1, 2});
+                        checked_set(y, ty, not_a_2digit_year, is);
+                        checked_set(m, tm, not_a_month, is);
+                        checked_set(d, td, not_a_day, is);
+#endif
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'X':
+                if (command)
+                {
+                    if (modified != CharT{'O'})
+                    {
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            checked_set(H, tm.tm_hour, not_a_hour, is);
+                            checked_set(M, tm.tm_min, not_a_minute, is);
+                            checked_set(s, duration_cast<Duration>(seconds{tm.tm_sec}),
+                                        not_a_second, is);
+                        }
+                        is.setstate(err);
+#else
+                        // "%T"
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        int tH = not_a_hour;
+                        int tM = not_a_minute;
+                        long double S{};
+                        read(is, ru{tH, 1, 2}, CharT{':'}, ru{tM, 1, 2},
+                                               CharT{':'}, rld{S, 1, w});
+                        checked_set(H, tH, not_a_hour, is);
+                        checked_set(M, tM, not_a_minute, is);
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+#endif
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'C':
+                if (command)
+                {
+                    int tC = not_a_century;
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+                    {
+#endif
+                        read(is, rs{tC, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+#if !ONLY_C_LOCALE
+                    }
+                    else
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            auto tY = tm.tm_year + 1900;
+                            tC = (tY >= 0 ? tY : tY-99) / 100;
+                        }
+                        is.setstate(err);
+                    }
+#endif
+                    checked_set(C, tC, not_a_century, is);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'D':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tn = not_a_month;
+                        int td = not_a_day;
+                        int ty = not_a_2digit_year;
+                        read(is, ru{tn, 1, 2}, CharT{'\0'}, CharT{'/'}, CharT{'\0'},
+                                 ru{td, 1, 2}, CharT{'\0'}, CharT{'/'}, CharT{'\0'},
+                                 rs{ty, 1, 2});
+                        checked_set(y, ty, not_a_2digit_year, is);
+                        checked_set(m, tn, not_a_month, is);
+                        checked_set(d, td, not_a_day, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'F':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tY = not_a_year;
+                        int tn = not_a_month;
+                        int td = not_a_day;
+                        read(is, rs{tY, 1, width == -1 ? 4u : static_cast<unsigned>(width)},
+                                 CharT{'-'}, ru{tn, 1, 2}, CharT{'-'}, ru{td, 1, 2});
+                        checked_set(Y, tY, not_a_year, is);
+                        checked_set(m, tn, not_a_month, is);
+                        checked_set(d, td, not_a_day, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'd':
+            case 'e':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'E'})
+#endif
+                    {
+                        int td = not_a_day;
+                        read(is, rs{td, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(d, td, not_a_day, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        command = nullptr;
+                        width = -1;
+                        modified = CharT{};
+                        if ((err & ios::failbit) == 0)
+                            checked_set(d, tm.tm_mday, not_a_day, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'H':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'E'})
+#endif
+                    {
+                        int tH = not_a_hour;
+                        read(is, ru{tH, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(H, tH, not_a_hour, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(H, tm.tm_hour, not_a_hour, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'I':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tI = not_a_hour_12_value;
+                        // reads in an hour into I, but most be in [1, 12]
+                        read(is, rs{tI, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        if (!(1 <= tI && tI <= 12))
+                            is.setstate(ios::failbit);
+                        checked_set(I, tI, not_a_hour_12_value, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+               break;
+            case 'j':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tj = not_a_doy;
+                        read(is, ru{tj, 1, width == -1 ? 3u : static_cast<unsigned>(width)});
+                        checked_set(j, tj, not_a_doy, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'M':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'E'})
+#endif
+                    {
+                        int tM = not_a_minute;
+                        read(is, ru{tM, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(M, tM, not_a_minute, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(M, tm.tm_min, not_a_minute, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'm':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'E'})
+#endif
+                    {
+                        int tn = not_a_month;
+                        read(is, rs{tn, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(m, tn, not_a_month, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(m, tm.tm_mon + 1, not_a_month, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'n':
+            case 't':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        // %n matches a single white space character
+                        // %t matches 0 or 1 white space characters
+                        auto ic = is.peek();
+                        if (Traits::eq_int_type(ic, Traits::eof()))
+                        {
+                            ios::iostate err = ios::eofbit;
+                            if (*fmt == 'n')
+                                err |= ios::failbit;
+                            is.setstate(err);
+                            break;
+                        }
+                        if (isspace(ic))
+                        {
+                            (void)is.get();
+                        }
+                        else if (*fmt == 'n')
+                            is.setstate(ios::failbit);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'p':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tp = not_a_ampm;
+#if !ONLY_C_LOCALE
+                        tm = std::tm{};
+                        tm.tm_hour = 1;
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        is.setstate(err);
+                        if (tm.tm_hour == 1)
+                            tp = 0;
+                        else if (tm.tm_hour == 13)
+                            tp = 1;
+                        else
+                            is.setstate(err);
+#else
+                        auto nm = detail::ampm_names();
+                        auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        tp = static_cast<decltype(tp)>(i);
+#endif
+                        checked_set(p, tp, not_a_ampm, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+
+               break;
+            case 'r':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            checked_set(H, tm.tm_hour, not_a_hour, is);
+                            checked_set(M, tm.tm_min, not_a_hour, is);
+                            checked_set(s, duration_cast<Duration>(seconds{tm.tm_sec}),
+                                        not_a_second, is);
+                        }
+                        is.setstate(err);
+#else
+                        // "%I:%M:%S %p"
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        long double S{};
+                        int tI = not_a_hour_12_value;
+                        int tM = not_a_minute;
+                        read(is, ru{tI, 1, 2}, CharT{':'}, ru{tM, 1, 2},
+                                               CharT{':'}, rld{S, 1, w});
+                        checked_set(I, tI, not_a_hour_12_value, is);
+                        checked_set(M, tM, not_a_minute, is);
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+                        ws(is);
+                        auto nm = detail::ampm_names();
+                        auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        checked_set(p, static_cast<int>(i), not_a_ampm, is);
+#endif
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'R':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tH = not_a_hour;
+                        int tM = not_a_minute;
+                        read(is, ru{tH, 1, 2}, CharT{'\0'}, CharT{':'}, CharT{'\0'},
+                                 ru{tM, 1, 2}, CharT{'\0'});
+                        checked_set(H, tH, not_a_hour, is);
+                        checked_set(M, tM, not_a_minute, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'S':
+                if (command)
+                {
+ #if !ONLY_C_LOCALE
+                   if (modified == CharT{})
+#else
+                   if (modified != CharT{'E'})
+#endif
+                    {
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        long double S{};
+                        read(is, rld{S, 1, width == -1 ? w : static_cast<unsigned>(width)});
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(s, duration_cast<Duration>(seconds{tm.tm_sec}),
+                                        not_a_second, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'T':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        int tH = not_a_hour;
+                        int tM = not_a_minute;
+                        long double S{};
+                        read(is, ru{tH, 1, 2}, CharT{':'}, ru{tM, 1, 2},
+                                               CharT{':'}, rld{S, 1, w});
+                        checked_set(H, tH, not_a_hour, is);
+                        checked_set(M, tM, not_a_minute, is);
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'Y':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'O'})
+#endif
+                    {
+                        int tY = not_a_year;
+                        read(is, rs{tY, 1, width == -1 ? 4u : static_cast<unsigned>(width)});
+                        checked_set(Y, tY, not_a_year, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'E'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(Y, tm.tm_year + 1900, not_a_year, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'y':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        int ty = not_a_2digit_year;
+                        read(is, ru{ty, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(y, ty, not_a_2digit_year, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(Y, tm.tm_year + 1900, not_a_year, is);
+                        is.setstate(err);
+                    }
+#endif
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'g':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tg = not_a_2digit_year;
+                        read(is, ru{tg, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(g, tg, not_a_2digit_year, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'G':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tG = not_a_year;
+                        read(is, rs{tG, 1, width == -1 ? 4u : static_cast<unsigned>(width)});
+                        checked_set(G, tG, not_a_year, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'U':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tU = not_a_week_num;
+                        read(is, ru{tU, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(U, tU, not_a_week_num, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'V':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tV = not_a_week_num;
+                        read(is, ru{tV, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(V, tV, not_a_week_num, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'W':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tW = not_a_week_num;
+                        read(is, ru{tW, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(W, tW, not_a_week_num, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'E':
+            case 'O':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        modified = *fmt;
+                    }
+                    else
+                    {
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                        command = nullptr;
+                        width = -1;
+                        modified = CharT{};
+                    }
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case '%':
+                if (command)
+                {
+                    if (modified == CharT{})
+                        read(is, *fmt);
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    command = fmt;
+                break;
+            case 'z':
+                if (command)
+                {
+                    int tH, tM;
+                    minutes toff = not_a_offset;
+                    bool neg = false;
+                    auto ic = is.peek();
+                    if (!Traits::eq_int_type(ic, Traits::eof()))
+                    {
+                        auto c = static_cast<char>(Traits::to_char_type(ic));
+                        if (c == '-')
+                            neg = true;
+                    }
+                    if (modified == CharT{})
+                    {
+                        read(is, rs{tH, 2, 2});
+                        if (!is.fail())
+                            toff = hours{std::abs(tH)};
+                        if (is.good())
+                        {
+                            ic = is.peek();
+                            if (!Traits::eq_int_type(ic, Traits::eof()))
+                            {
+                                auto c = static_cast<char>(Traits::to_char_type(ic));
+                                if ('0' <= c && c <= '9')
+                                {
+                                    read(is, ru{tM, 2, 2});
+                                    if (!is.fail())
+                                        toff += minutes{tM};
+                                }
+                            }
+                        }
+                    }
+                    else
+                    {
+                        read(is, rs{tH, 1, 2});
+                        if (!is.fail())
+                            toff = hours{std::abs(tH)};
+                        if (is.good())
+                        {
+                            ic = is.peek();
+                            if (!Traits::eq_int_type(ic, Traits::eof()))
+                            {
+                                auto c = static_cast<char>(Traits::to_char_type(ic));
+                                if (c == ':')
+                                {
+                                    (void)is.get();
+                                    read(is, ru{tM, 2, 2});
+                                    if (!is.fail())
+                                        toff += minutes{tM};
+                                }
+                            }
+                        }
+                    }
+                    if (neg)
+                        toff = -toff;
+                    checked_set(temp_offset, toff, not_a_offset, is);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'Z':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        std::basic_string<CharT, Traits, Alloc> buf;
+                        while (is.rdstate() == std::ios::goodbit)
+                        {
+                            auto i = is.rdbuf()->sgetc();
+                            if (Traits::eq_int_type(i, Traits::eof()))
+                            {
+                                is.setstate(ios::eofbit);
+                                break;
+                            }
+                            auto wc = Traits::to_char_type(i);
+                            auto c = static_cast<char>(wc);
+                            // is c a valid time zone name or abbreviation character?
+                            if (!(CharT{1} < wc && wc < CharT{127}) || !(isalnum(c) ||
+                                    c == '_' || c == '/' || c == '-' || c == '+'))
+                                break;
+                            buf.push_back(c);
+                            is.rdbuf()->sbumpc();
+                        }
+                        if (buf.empty())
+                            is.setstate(ios::failbit);
+                        checked_set(temp_abbrev, buf, {}, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            default:
+                if (command)
+                {
+                    if (width == -1 && modified == CharT{} && '0' <= *fmt && *fmt <= '9')
+                    {
+                        width = static_cast<char>(*fmt) - '0';
+                        while ('0' <= fmt[1] && fmt[1] <= '9')
+                            width = 10*width + static_cast<char>(*++fmt) - '0';
+                    }
+                    else
+                    {
+                        if (modified == CharT{})
+                            read(is, CharT{'%'}, width, *fmt);
+                        else
+                            read(is, CharT{'%'}, width, modified, *fmt);
+                        command = nullptr;
+                        width = -1;
+                        modified = CharT{};
+                    }
+                }
+                else  // !command
+                {
+                    if (isspace(static_cast<unsigned char>(*fmt)))
+                    {
+                        // space matches 0 or more white space characters
+                        if (is.good())
+                           ws(is);
+                    }
+                    else
+                        read(is, *fmt);
+                }
+                break;
+            }
+        }
+        // is.fail() || *fmt == CharT{}
+        if (is.rdstate() == ios::goodbit && command)
+        {
+            if (modified == CharT{})
+                read(is, CharT{'%'}, width);
+            else
+                read(is, CharT{'%'}, width, modified);
+        }
+        if (!is.fail())
+        {
+            if (y != not_a_2digit_year)
+            {
+                // Convert y and an optional C to Y
+                if (!(0 <= y && y <= 99))
+                    goto broken;
+                if (C == not_a_century)
+                {
+                    if (Y == not_a_year)
+                    {
+                        if (y >= 69)
+                            C = 19;
+                        else
+                            C = 20;
+                    }
+                    else
+                    {
+                        C = (Y >= 0 ? Y : Y-100) / 100;
+                    }
+                }
+                int tY;
+                if (C >= 0)
+                    tY = 100*C + y;
+                else
+                    tY = 100*(C+1) - (y == 0 ? 100 : y);
+                if (Y != not_a_year && Y != tY)
+                    goto broken;
+                Y = tY;
+            }
+            if (g != not_a_2digit_year)
+            {
+                // Convert g and an optional C to G
+                if (!(0 <= g && g <= 99))
+                    goto broken;
+                if (C == not_a_century)
+                {
+                    if (G == not_a_year)
+                    {
+                        if (g >= 69)
+                            C = 19;
+                        else
+                            C = 20;
+                    }
+                    else
+                    {
+                        C = (G >= 0 ? G : G-100) / 100;
+                    }
+                }
+                int tG;
+                if (C >= 0)
+                    tG = 100*C + g;
+                else
+                    tG = 100*(C+1) - (g == 0 ? 100 : g);
+                if (G != not_a_year && G != tG)
+                    goto broken;
+                G = tG;
+            }
+            if (Y < static_cast<int>(year::min()) || Y > static_cast<int>(year::max()))
+                Y = not_a_year;
+            bool computed = false;
+            if (G != not_a_year && V != not_a_week_num && wd != not_a_weekday)
+            {
+                year_month_day ymd_trial = sys_days(year{G-1}/December/Thursday[last]) +
+                                           (Monday-Thursday) + weeks{V-1} +
+                                           (weekday{static_cast<unsigned>(wd)}-Monday);
+                if (Y == not_a_year)
+                    Y = static_cast<int>(ymd_trial.year());
+                else if (year{Y} != ymd_trial.year())
+                    goto broken;
+                if (m == not_a_month)
+                    m = static_cast<int>(static_cast<unsigned>(ymd_trial.month()));
+                else if (month(static_cast<unsigned>(m)) != ymd_trial.month())
+                    goto broken;
+                if (d == not_a_day)
+                    d = static_cast<int>(static_cast<unsigned>(ymd_trial.day()));
+                else if (day(static_cast<unsigned>(d)) != ymd_trial.day())
+                    goto broken;
+                computed = true;
+            }
+            if (Y != not_a_year && U != not_a_week_num && wd != not_a_weekday)
+            {
+                year_month_day ymd_trial = sys_days(year{Y}/January/Sunday[1]) +
+                                           weeks{U-1} +
+                                           (weekday{static_cast<unsigned>(wd)} - Sunday);
+                if (Y == not_a_year)
+                    Y = static_cast<int>(ymd_trial.year());
+                else if (year{Y} != ymd_trial.year())
+                    goto broken;
+                if (m == not_a_month)
+                    m = static_cast<int>(static_cast<unsigned>(ymd_trial.month()));
+                else if (month(static_cast<unsigned>(m)) != ymd_trial.month())
+                    goto broken;
+                if (d == not_a_day)
+                    d = static_cast<int>(static_cast<unsigned>(ymd_trial.day()));
+                else if (day(static_cast<unsigned>(d)) != ymd_trial.day())
+                    goto broken;
+                computed = true;
+            }
+            if (Y != not_a_year && W != not_a_week_num && wd != not_a_weekday)
+            {
+                year_month_day ymd_trial = sys_days(year{Y}/January/Monday[1]) +
+                                           weeks{W-1} +
+                                           (weekday{static_cast<unsigned>(wd)} - Monday);
+                if (Y == not_a_year)
+                    Y = static_cast<int>(ymd_trial.year());
+                else if (year{Y} != ymd_trial.year())
+                    goto broken;
+                if (m == not_a_month)
+                    m = static_cast<int>(static_cast<unsigned>(ymd_trial.month()));
+                else if (month(static_cast<unsigned>(m)) != ymd_trial.month())
+                    goto broken;
+                if (d == not_a_day)
+                    d = static_cast<int>(static_cast<unsigned>(ymd_trial.day()));
+                else if (day(static_cast<unsigned>(d)) != ymd_trial.day())
+                    goto broken;
+                computed = true;
+            }
+            if (j != not_a_doy && Y != not_a_year)
+            {
+                auto ymd_trial = year_month_day{local_days(year{Y}/1/1) + days{j-1}};
+                if (m == not_a_month)
+                    m = static_cast<int>(static_cast<unsigned>(ymd_trial.month()));
+                else if (month(static_cast<unsigned>(m)) != ymd_trial.month())
+                    goto broken;
+                if (d == not_a_day)
+                    d = static_cast<int>(static_cast<unsigned>(ymd_trial.day()));
+                else if (day(static_cast<unsigned>(d)) != ymd_trial.day())
+                    goto broken;
+                j = not_a_doy;
+            }
+            auto ymd = year{Y}/m/d;
+            if (ymd.ok())
+            {
+                if (wd == not_a_weekday)
+                    wd = static_cast<int>((weekday(sys_days(ymd)) - Sunday).count());
+                else if (wd != static_cast<int>((weekday(sys_days(ymd)) - Sunday).count()))
+                    goto broken;
+                if (!computed)
+                {
+                    if (G != not_a_year || V != not_a_week_num)
+                    {
+                        sys_days sd = ymd;
+                        auto G_trial = year_month_day{sd + days{3}}.year();
+                        auto start = sys_days((G_trial - years{1})/December/Thursday[last]) +
+                                     (Monday - Thursday);
+                        if (sd < start)
+                        {
+                            --G_trial;
+                            if (V != not_a_week_num)
+                                start = sys_days((G_trial - years{1})/December/Thursday[last])
+                                        + (Monday - Thursday);
+                        }
+                        if (G != not_a_year && G != static_cast<int>(G_trial))
+                            goto broken;
+                        if (V != not_a_week_num)
+                        {
+                            auto V_trial = duration_cast<weeks>(sd - start).count() + 1;
+                            if (V != V_trial)
+                                goto broken;
+                        }
+                    }
+                    if (U != not_a_week_num)
+                    {
+                        auto start = sys_days(Sunday[1]/January/ymd.year());
+                        auto U_trial = floor<weeks>(sys_days(ymd) - start).count() + 1;
+                        if (U != U_trial)
+                            goto broken;
+                    }
+                    if (W != not_a_week_num)
+                    {
+                        auto start = sys_days(Monday[1]/January/ymd.year());
+                        auto W_trial = floor<weeks>(sys_days(ymd) - start).count() + 1;
+                        if (W != W_trial)
+                            goto broken;
+                    }
+                }
+            }
+            fds.ymd = ymd;
+            if (I != not_a_hour_12_value)
+            {
+                if (!(1 <= I && I <= 12))
+                    goto broken;
+                if (p != not_a_ampm)
+                {
+                    // p is in [0, 1] == [AM, PM]
+                    // Store trial H in I
+                    if (I == 12)
+                        --p;
+                    I += p*12;
+                    // Either set H from I or make sure H and I are consistent
+                    if (H == not_a_hour)
+                        H = I;
+                    else if (I != H)
+                        goto broken;
+                }
+                else  // p == not_a_ampm
+                {
+                    // if H, make sure H and I could be consistent
+                    if (H != not_a_hour)
+                    {
+                        if (I == 12)
+                        {
+                            if (H != 0 && H != 12)
+                                goto broken;
+                        }
+                        else if (!(I == H || I == H+12))
+                        {
+                            goto broken;
+                        }
+                    }
+                    else  // I is ambiguous, AM or PM?
+                        goto broken;
+                }
+            }
+            if (H != not_a_hour)
+            {
+                fds.has_tod = true;
+                fds.tod = hh_mm_ss<Duration>{hours{H}};
+            }
+            if (M != not_a_minute)
+            {
+                fds.has_tod = true;
+                fds.tod.m_ = minutes{M};
+            }
+            if (s != not_a_second)
+            {
+                fds.has_tod = true;
+                fds.tod.s_ = detail::decimal_format_seconds<Duration>{s};
+            }
+            if (j != not_a_doy)
+            {
+                fds.has_tod = true;
+                fds.tod.h_ += hours{days{j}};
+            }
+            if (wd != not_a_weekday)
+                fds.wd = weekday{static_cast<unsigned>(wd)};
+            if (abbrev != nullptr)
+                *abbrev = std::move(temp_abbrev);
+            if (offset != nullptr && temp_offset != not_a_offset)
+              *offset = temp_offset;
+        }
+       return is;
+    }
+broken:
+    is.setstate(ios::failbit);
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, year& y,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    date::from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.year().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        y = fds.ymd.year();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, month& m,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    date::from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.month().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        m = fds.ymd.month();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, day& d,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    date::from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.day().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        d = fds.ymd.day();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, weekday& wd,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    date::from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.wd.ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        wd = fds.wd;
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, year_month& ym,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    date::from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.month().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        ym = fds.ymd.year()/fds.ymd.month();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, month_day& md,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    date::from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.month().ok() || !fds.ymd.day().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        md = fds.ymd.month()/fds.ymd.day();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            year_month_day& ymd, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    date::from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        ymd = fds.ymd;
+    return is;
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            sys_time<Duration>& tp, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    using detail::round_i;
+    std::chrono::minutes offset_local{};
+    auto offptr = offset ? offset : &offset_local;
+    fields<CT> fds{};
+    fds.has_tod = true;
+    date::from_stream(is, fmt, fds, abbrev, offptr);
+    if (!fds.ymd.ok() || !fds.tod.in_conventional_range())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        tp = round_i<Duration>(sys_days(fds.ymd) - *offptr + fds.tod.to_duration());
+    return is;
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            local_time<Duration>& tp, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    using detail::round_i;
+    fields<CT> fds{};
+    fds.has_tod = true;
+    date::from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.ok() || !fds.tod.in_conventional_range())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        tp = round_i<Duration>(local_seconds{local_days(fds.ymd)} + fds.tod.to_duration());
+    return is;
+}
+
+template <class Rep, class Period, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            std::chrono::duration<Rep, Period>& d,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using Duration = std::chrono::duration<Rep, Period>;
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    using detail::round_i;
+    fields<CT> fds{};
+    date::from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.has_tod)
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        d = round_i<Duration>(fds.tod.to_duration());
+    return is;
+}
+
+template <class Parsable, class CharT, class Traits = std::char_traits<CharT>,
+          class Alloc = std::allocator<CharT>>
+struct parse_manip
+{
+    const std::basic_string<CharT, Traits, Alloc> format_;
+    Parsable&                                     tp_;
+    std::basic_string<CharT, Traits, Alloc>*      abbrev_;
+    std::chrono::minutes*                         offset_;
+
+public:
+    parse_manip(std::basic_string<CharT, Traits, Alloc> format, Parsable& tp,
+                std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+                std::chrono::minutes* offset = nullptr)
+        : format_(std::move(format))
+        , tp_(tp)
+        , abbrev_(abbrev)
+        , offset_(offset)
+        {}
+
+#if HAS_STRING_VIEW
+    parse_manip(const CharT* format, Parsable& tp,
+                std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+                std::chrono::minutes* offset = nullptr)
+        : format_(format)
+        , tp_(tp)
+        , abbrev_(abbrev)
+        , offset_(offset)
+        {}
+
+    parse_manip(std::basic_string_view<CharT, Traits> format, Parsable& tp,
+                std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+                std::chrono::minutes* offset = nullptr)
+        : format_(format)
+        , tp_(tp)
+        , abbrev_(abbrev)
+        , offset_(offset)
+        {}
+#endif  // HAS_STRING_VIEW
+};
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+std::basic_istream<CharT, Traits>&
+operator>>(std::basic_istream<CharT, Traits>& is,
+           const parse_manip<Parsable, CharT, Traits, Alloc>& x)
+{
+    return date::from_stream(is, x.format_.c_str(), x.tp_, x.abbrev_, x.offset_);
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const std::basic_string<CharT, Traits, Alloc>& format, Parsable& tp)
+    -> decltype(date::from_stream(std::declval<std::basic_istream<CharT, Traits>&>(),
+                            format.c_str(), tp),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp})
+{
+    return {format, tp};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const std::basic_string<CharT, Traits, Alloc>& format, Parsable& tp,
+      std::basic_string<CharT, Traits, Alloc>& abbrev)
+    -> decltype(date::from_stream(std::declval<std::basic_istream<CharT, Traits>&>(),
+                            format.c_str(), tp, &abbrev),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, &abbrev})
+{
+    return {format, tp, &abbrev};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const std::basic_string<CharT, Traits, Alloc>& format, Parsable& tp,
+      std::chrono::minutes& offset)
+    -> decltype(date::from_stream(std::declval<std::basic_istream<CharT, Traits>&>(),
+                            format.c_str(), tp,
+                            std::declval<std::basic_string<CharT, Traits, Alloc>*>(),
+                            &offset),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, nullptr, &offset})
+{
+    return {format, tp, nullptr, &offset};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const std::basic_string<CharT, Traits, Alloc>& format, Parsable& tp,
+      std::basic_string<CharT, Traits, Alloc>& abbrev, std::chrono::minutes& offset)
+    -> decltype(date::from_stream(std::declval<std::basic_istream<CharT, Traits>&>(),
+                            format.c_str(), tp, &abbrev, &offset),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, &abbrev, &offset})
+{
+    return {format, tp, &abbrev, &offset};
+}
+
+// const CharT* formats
+
+template <class Parsable, class CharT>
+inline
+auto
+parse(const CharT* format, Parsable& tp)
+    -> decltype(date::from_stream(std::declval<std::basic_istream<CharT>&>(), format, tp),
+                parse_manip<Parsable, CharT>{format, tp})
+{
+    return {format, tp};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const CharT* format, Parsable& tp, std::basic_string<CharT, Traits, Alloc>& abbrev)
+    -> decltype(date::from_stream(std::declval<std::basic_istream<CharT, Traits>&>(), format,
+                            tp, &abbrev),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, &abbrev})
+{
+    return {format, tp, &abbrev};
+}
+
+template <class Parsable, class CharT>
+inline
+auto
+parse(const CharT* format, Parsable& tp, std::chrono::minutes& offset)
+    -> decltype(date::from_stream(std::declval<std::basic_istream<CharT>&>(), format,
+                            tp, std::declval<std::basic_string<CharT>*>(), &offset),
+                parse_manip<Parsable, CharT>{format, tp, nullptr, &offset})
+{
+    return {format, tp, nullptr, &offset};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const CharT* format, Parsable& tp,
+      std::basic_string<CharT, Traits, Alloc>& abbrev, std::chrono::minutes& offset)
+    -> decltype(date::from_stream(std::declval<std::basic_istream<CharT, Traits>&>(), format,
+                            tp, &abbrev, &offset),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, &abbrev, &offset})
+{
+    return {format, tp, &abbrev, &offset};
+}
+
+// duration streaming
+
+template <class CharT, class Traits, class Rep, class Period>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os,
+           const std::chrono::duration<Rep, Period>& d)
+{
+    return os << detail::make_string<CharT, Traits>::from(d.count()) +
+                 detail::get_units<CharT>(typename Period::type{});
+}
+
+}  // namespace date
+
+#ifdef _MSC_VER
+#   pragma warning(pop)
+#endif
+
+#ifdef __GNUC__
+# pragma GCC diagnostic pop
+#endif
+
+// NOLINTEND
+// clang-format off
+
+#endif  // DATE_H
diff --git a/redfish-core/include/utils/time_utils.hpp b/redfish-core/include/utils/time_utils.hpp
index 314ea85..fbee6ce 100644
--- a/redfish-core/include/utils/time_utils.hpp
+++ b/redfish-core/include/utils/time_utils.hpp
@@ -2,8 +2,6 @@
 
 #include "logging.hpp"
 
-#include <boost/date_time.hpp>
-
 #include <algorithm>
 #include <charconv>
 #include <chrono>
@@ -420,30 +418,6 @@
 }
 
 using usSinceEpoch = std::chrono::duration<uint64_t, std::micro>;
-inline std::optional<usSinceEpoch> dateStringToEpoch(std::string_view datetime)
-{
-    std::string date(datetime);
-    std::stringstream stream(date);
-    // Convert from ISO 8601 to boost local_time
-    // (BMC only has time in UTC)
-    boost::posix_time::ptime posixTime;
-    boost::posix_time::ptime epoch(boost::gregorian::date(1970, 1, 1));
-    // Facet gets deleted with the stringsteam
-    auto ifc = std::make_unique<boost::local_time::local_time_input_facet>(
-        "%Y-%m-%d %H:%M:%S%F %ZP");
-    stream.imbue(std::locale(stream.getloc(), ifc.release()));
-
-    boost::local_time::local_date_time ldt(boost::local_time::not_a_date_time);
-
-    if (!(stream >> ldt))
-    {
-        return std::nullopt;
-    }
-    posixTime = ldt.utc_time();
-    boost::posix_time::time_duration dur = posixTime - epoch;
-    uint64_t durMicroSecs = static_cast<uint64_t>(dur.total_microseconds());
-    return std::chrono::duration<uint64_t, std::micro>{durMicroSecs};
-}
-
+std::optional<usSinceEpoch> dateStringToEpoch(std::string_view datetime);
 } // namespace time_utils
 } // namespace redfish
diff --git a/redfish-core/src/utils/time_utils.cpp b/redfish-core/src/utils/time_utils.cpp
new file mode 100644
index 0000000..f427ba6
--- /dev/null
+++ b/redfish-core/src/utils/time_utils.cpp
@@ -0,0 +1,44 @@
+#include "utils/time_utils.hpp"
+
+#include "utils/extern/date.h"
+
+#include <array>
+#include <chrono>
+#include <optional>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <version>
+
+namespace redfish::time_utils
+{
+using usSinceEpoch = std::chrono::duration<uint64_t, std::micro>;
+std::optional<usSinceEpoch> dateStringToEpoch(std::string_view datetime)
+{
+    for (const char* format : std::to_array({"%FT%T%Ez", "%FT%TZ", "%FT%T"}))
+    {
+        // Parse using signed so we can detect negative dates
+        std::chrono::sys_time<std::chrono::duration<int64_t, std::micro>> date;
+        std::istringstream iss(std::string{datetime});
+#if __cpp_lib_chrono >= 201907L
+        namespace chrono_from_stream = std::chrono;
+#else
+        namespace chrono_from_stream = date;
+#endif
+        if (chrono_from_stream::from_stream(iss, format, date))
+        {
+            if (date.time_since_epoch().count() < 0)
+            {
+                return std::nullopt;
+            }
+            if (iss.rdbuf()->in_avail() != 0)
+            {
+                // More information left at end of string.
+                continue;
+            }
+            return usSinceEpoch{date.time_since_epoch().count()};
+        }
+    }
+    return std::nullopt;
+}
+} // namespace redfish::time_utils
diff --git a/test/redfish-core/include/utils/time_utils_test.cpp b/test/redfish-core/include/utils/time_utils_test.cpp
index 873a385..e88f758 100644
--- a/test/redfish-core/include/utils/time_utils_test.cpp
+++ b/test/redfish-core/include/utils/time_utils_test.cpp
@@ -166,9 +166,8 @@
               usSinceEpoch{253402300799999999});
 
     // Underflow
-    // Currently gives wrong result
-    // EXPECT_EQ(dateStringToEpoch("1969-12-30T23:59:59.999999+00:00"),
-    //          std::nullopt);
+    EXPECT_EQ(dateStringToEpoch("1969-12-30T23:59:59.999999+00:00"),
+              std::nullopt);
 }
 
 } // namespace