hashing utility for register and node IDs
Signed-off-by: Zane Shelley <zshelle@us.ibm.com>
Change-Id: I69ac08e875982456fe81c7e65b1135411f25af81
diff --git a/src/hei_util.hpp b/src/hei_util.hpp
new file mode 100644
index 0000000..5db544c
--- /dev/null
+++ b/src/hei_util.hpp
@@ -0,0 +1,70 @@
+#pragma once
+
+#include <assert.h>
+
+#include <hei_types.hpp>
+
+#include <limits>
+#include <string>
+
+namespace libhei
+{
+
+//------------------------------------------------------------------------------
+
+/**
+ * @brief The string hashing algorithm used for register and isolation node
+ * names.
+ */
+inline uint64_t hash(unsigned int i_bytes, const std::string& i_str)
+{
+ // This hash is a simple "n*s[0] + (n-1)*s[1] + ... + s[n-1]" algorithm,
+ // where s[i] is a chunk from the input string the length of i_bytes.
+
+ // Currently only supporting 1-8 byte hashes.
+ assert(1 <= i_bytes && i_bytes <= sizeof(uint64_t));
+
+ // Start hashing each chunk.
+ uint64_t sumA = 0;
+ uint64_t sumB = 0;
+
+ // Iterate one chunk at a time.
+ for (unsigned int i = 0; i < i_str.size(); i += i_bytes)
+ {
+ // Combine each chunk into a single integer value. If we reach the end
+ // of the string, pad with null characters.
+ uint64_t chunk = 0;
+ for (unsigned int j = 0; j < i_bytes; j++)
+ {
+ chunk <<= 8;
+ chunk |= (i + j < i_str.size()) ? i_str[i + j] : '\0';
+ }
+
+ // Apply the simple hash.
+ sumA += chunk;
+ sumB += sumA;
+ }
+
+ // Mask off everything except the target number of bytes.
+ auto mask = std::numeric_limits<uint64_t>::max();
+ sumB &= mask >> ((sizeof(uint64_t) - i_bytes) * 8);
+
+ return sumB;
+}
+
+template <class T>
+inline T hash(const std::string& i_str)
+{
+ return static_cast<T>(hash(sizeof(T), i_str));
+}
+
+// Specialization for RegisterId_t because they are only a 3-byte field.
+template <>
+inline RegisterId_t hash<RegisterId_t>(const std::string& i_str)
+{
+ return static_cast<RegisterId_t>(hash(3, i_str));
+}
+
+//------------------------------------------------------------------------------
+
+} // namespace libhei
diff --git a/test/meson.build b/test/meson.build
index cbe7fbc..2025c64 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -32,6 +32,7 @@
'bit_string_test',
'flyweight_test',
'operator_register_test',
+ 'test-util-hash',
]
foreach g : gtests
diff --git a/test/test-util-hash.cpp b/test/test-util-hash.cpp
new file mode 100644
index 0000000..ba35625
--- /dev/null
+++ b/test/test-util-hash.cpp
@@ -0,0 +1,24 @@
+#include <hei_util.hpp>
+
+#include "gtest/gtest.h"
+
+using namespace libhei;
+
+TEST(UtilHash, TestSet1)
+{
+ std::string s{"SOME_RANDOM_STRING"};
+
+ uint8_t h1 = 0xBE;
+ uint16_t h2 = 0xF2DD;
+ uint32_t h3 = 0xDFB31440;
+ uint64_t h4 = 0xD0D3828Ec49F687C;
+ NodeId_t h5 = 0xF2DD; // 2-byte field
+ RegisterId_t h6 = static_cast<RegisterId_t>(0x31D080); // 3-byte field
+
+ EXPECT_EQ(h1, hash<uint8_t>(s));
+ EXPECT_EQ(h2, hash<uint16_t>(s));
+ EXPECT_EQ(h3, hash<uint32_t>(s));
+ EXPECT_EQ(h4, hash<uint64_t>(s));
+ EXPECT_EQ(h5, hash<NodeId_t>(s));
+ EXPECT_EQ(h6, hash<RegisterId_t>(s));
+}