Add algorithm for Residual Echo Detector.

webrtc/modules/audio_processing/echo_detector/circular_buffer.cc

Index: webrtc/modules/audio_processing/echo_detector/circular_buffer.cc
diff --git a/webrtc/modules/audio_processing/echo_detector/circular_buffer.cc b/webrtc/modules/audio_processing/echo_detector/circular_buffer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4a77a99bc2a3572157e7316cdbcac0bf435d1f5c
--- /dev/null
+++ b/webrtc/modules/audio_processing/echo_detector/circular_buffer.cc
@@ -0,0 +1,48 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/audio_processing/echo_detector/circular_buffer.h"
+
+#include <algorithm>
+
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+
+CircularBuffer::CircularBuffer(size_t size) : buffer_(size) {}
+CircularBuffer::~CircularBuffer() = default;
+
+void CircularBuffer::Push(float value) {
+  buffer_[next_insertion_index_] = value;
+  ++next_insertion_index_;
+  next_insertion_index_ %= buffer_.size();
+  RTC_DCHECK_LT(next_insertion_index_, buffer_.size());
+  buffer_size_ = std::min(buffer_size_ + 1, buffer_.size());
+  RTC_DCHECK_LE(buffer_size_, buffer_.size());

[peah-webrtc, 2016/10/27 14:27:09]

It is quite easy to mix up buffer_size_ and buffer_.size() and not easy to
explain the difference between these. Suggestion: Can you somehow change the
name of buffer_size_ to avoid this?

+}
+
+rtc::Optional<float> CircularBuffer::Pop() {
+  if (buffer_size_ == 0) {
+    return rtc::Optional<float>();
+  }
+  const size_t index =
+      (buffer_.size() + next_insertion_index_ - buffer_size_) % buffer_.size();
+  RTC_DCHECK_LT(index, buffer_.size());
+  --buffer_size_;
+  return rtc::Optional<float>(buffer_[index]);
+}
+
+void CircularBuffer::Clear() {
+  std::fill(buffer_.begin(), buffer_.end(), 0.f);
+  next_insertion_index_ = 0;
+  buffer_size_ = 0;
+}
+
+}  // namespace webrtc