Add algorithm for Residual Echo Detector.

webrtc/modules/audio_processing/echo_detector/circular_buffer.cc

+/*
+ *  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"
+#include "webrtc/base/logging.h"
+
+namespace webrtc {
+
+CircularBuffer::CircularBuffer(size_t size) : buffer_(size) {}
+CircularBuffer::CircularBuffer(CircularBuffer&& other) = default;
+CircularBuffer::~CircularBuffer() = default;
+
+void CircularBuffer::Insert(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());
+}
+
+float CircularBuffer::GetValue() {
+  if (buffer_size_ > 0) {
+    const size_t index =
+        (buffer_.size() + next_insertion_index_ - buffer_size_) %
+        buffer_.size();
+    RTC_DCHECK_LT(index, buffer_.size());
+    --buffer_size_;
+    return buffer_[index];
+  } else {

[hlundin-webrtc, 2016/10/17 18:49:39]

In these cases, where you have one large "good code path" and one small "error
code path", I prefer to exit early on error. That is:
if (buffer_size_ == 0) {
  LOG...;
  return 0.f;
}
// rest of code goes here...

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

Done.

+    LOG(LS_ERROR) << "Attempted to get value from buffer, but it was empty.";
+    return 0.f;

[hlundin-webrtc, 2016/10/17 18:49:39]

What will happens where this is used? Would it make sense to return an
Optional<float>, or will ut just mess up the calling code?

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

I thought this should not happen, but now I'm not sure if clock drift could
cause this to happen. I'll ask Per about it. Anyway, returning an optional is
probably a better idea than just returning zero, so I'll do that instead.

+  }
+}
+
+void CircularBuffer::Clear() {
+  std::fill(buffer_.begin(), buffer_.end(), 0.f);
+  next_insertion_index_ = 0;
+  buffer_size_ = 0;
+}
+
+}  // namespace webrtc