Add algorithm for Residual Echo Detector.

webrtc/modules/audio_processing/echo_detector/circular_buffer.h

Index: webrtc/modules/audio_processing/echo_detector/circular_buffer.h
diff --git a/webrtc/modules/audio_processing/echo_detector/circular_buffer.h b/webrtc/modules/audio_processing/echo_detector/circular_buffer.h
new file mode 100644
index 0000000000000000000000000000000000000000..db0d10161d90bf56fa45e510ab48667343a7cb5c
--- /dev/null
+++ b/webrtc/modules/audio_processing/echo_detector/circular_buffer.h
@@ -0,0 +1,38 @@
+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_CIRCULAR_BUFFER_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_CIRCULAR_BUFFER_H_
+
+#include <vector>
+
+namespace webrtc {
+
+// Ring buffer containing floating point values.
+struct CircularBuffer {
+ public:
+  explicit CircularBuffer(size_t size);
+  CircularBuffer(CircularBuffer&& other);
+  ~CircularBuffer();
+
+  void Insert(float value);
+  float GetValue();

[hlundin-webrtc, 2016/10/17 18:49:40]

I think this should be called Pop. This makes it clearer that values are
removed, and not just viewed. It also aligns with the terminology of STL. (You
may want to rename Insert to Push, but I consider that optional, as Insert is
quite clear in this context.)

[ivoc, 2016/10/18 15:20:19]

Done.

+  // This function fills the buffer with zeros, but does not change its size.
+  void Clear();
+
+ private:
+  std::vector<float> buffer_;
+  size_t next_insertion_index_ = 0;
+  size_t buffer_size_ = 0;

[hlundin-webrtc, 2016/10/17 18:49:40]

Please, comment that this is not the allocated size, but the number of elements
inserted.

[ivoc, 2016/10/18 15:20:19]

Done.

+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_CIRCULAR_BUFFER_H_