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..5d2b4c4881e529fa89f71dfa3a8adb30c55fa307
--- /dev/null
+++ b/webrtc/modules/audio_processing/echo_detector/circular_buffer.cc
@@ -0,0 +1,53 @@
+/*
+ *  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::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());
+}
+
+rtc::Optional<float> CircularBuffer::Pop() {
+  if (buffer_size_ == 0) {
+    LOG(LS_ERROR) << "Attempted to get value from buffer, but it was empty.";

[hlundin-webrtc, 2016/10/18 20:52:22]

Now you are logging the same error twice – here and where this is called from.
With the use of Optional, I would say that this is not an error in the
CircularBuffer per se, it just happened to be empty and thus return empty. 

[ivoc, 2016/10/19 14:12:04]

Good point, I will remove this one.

+    return rtc::Optional<float>();
+  } else {

[hlundin-webrtc, 2016/10/18 20:52:22]

You don't need the else here, since the if path returns. Let the remainder of
the function be on "function-level indentation", i.e.,

rtc::Optional<float> CircularBuffer::Pop() {
  if (odd_things) {
    // Deal with it.
    return rtc::Optional<float>();
  }

  // Life is good. Do awesome stuff, but with less indentation.
  return rtc::Optional<float>(awesome_result);
}

[ivoc, 2016/10/19 14:12:04]

Done.

+    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