Move circular buffer class from wpilib to wpiutil (#1840)

wpiutil/src/main/native/include/wpi/circular_buffer.h

@@ -0,0 +1,62 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2015-2019 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <cstddef>
+#include <vector>
+
+namespace wpi {
+
+/**
+ * This is a simple circular buffer so we don't need to "bucket brigade" copy
+ * old values.
+ */
+template <class T>
+class circular_buffer {
+ public:
+  explicit circular_buffer(size_t size);
+
+  using value_type = T;
+  using reference = value_type&;
+  using const_reference = const value_type&;
+  using pointer = value_type*;
+  using size_type = size_t;
+  using iterator_category = std::forward_iterator_tag;
+  using difference_type = std::ptrdiff_t;
+
+  size_type size() const;
+  T& front();
+  const T& front() const;
+  T& back();
+  const T& back() const;
+  void push_front(T value);
+  void push_back(T value);
+  T pop_front();
+  T pop_back();
+  void resize(size_t size);
+  void reset();
+
+  T& operator[](size_t index);
+  const T& operator[](size_t index) const;
+
+ private:
+  std::vector<T> m_data;
+
+  // Index of element at front of buffer
+  size_t m_front = 0;
+
+  // Number of elements used in buffer
+  size_t m_length = 0;
+
+  size_t ModuloInc(size_t index);
+  size_t ModuloDec(size_t index);
+};
+
+}  // namespace wpi
+
+#include "wpi/circular_buffer.inc"