diff --git a/bargraph.hpp b/bargraph.hpp
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+++ b/bargraph.hpp
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+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <stdio.h>
+
+#include <vector>
+
+template <typename ValueType>
+class BarGraph
+{
+  public:
+    std::vector<ValueType> history_; // is actually a ring buffer.
+    int next_;   // index to the slot where the next insertion will go
+    int length_; // total # of data points that have ever been added
+    explicit BarGraph(int capacity) : next_(0), length_(0)
+    {
+        history_.resize(capacity);
+        std::fill(history_.begin(), history_.end(), 0);
+    }
+
+    // The last value is in [0], so on and so forth
+    // Note: if there are not enough data, this function will return as much
+    // as is available
+    std::vector<float> GetLastNValues(int x)
+    {
+        std::vector<float> ret;
+        const int N = static_cast<int>(history_.size());
+        int imax = x;
+        imax = std::min(imax, length_);
+        imax = std::min(imax, N);
+        int idx = (next_ - 1 + N) % N;
+        for (int i = 0; i < imax; i++)
+        {
+            ret.push_back(history_[idx]);
+            idx = (idx - 1 + N) % N;
+        }
+        return ret;
+    }
+
+    void AddValue(ValueType x)
+    {
+        history_[next_] = x;
+        next_ = (next_ + 1) % history_.size();
+        length_++;
+    }
+};