Adding BlockMeanCalculator for AEC.

webrtc/modules/audio_processing/utility/block_mean_calculator.cc

+/*
+ *  Copyright 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/utility/block_mean_calculator.h"
+
+namespace webrtc {
+
+BlockMeanCalculator::BlockMeanCalculator(size_t block_length)
+    : block_length_(block_length),
+      count_(0),
+      sum_(0.0),
+      mean_(0.0) {
+}
+
+void BlockMeanCalculator::Reset() {
+  Clear();
+  mean_ = 0.0;
+}
+
+void BlockMeanCalculator::AddSample(float sample) {

[peah-webrtc, 2016/03/24 07:18:41]

I think it is better to not call this sample and the class is more general than
not just to apply to samples (and it is not used for storing samples in
aec_core.cc). What about value resp AddValue?

[minyue-webrtc, 2016/03/24 09:13:57]

Done.

+  sum_ += sample;
+  ++count_;
+  if (count_ == block_length_) {
+    mean_ = sum_ / block_length_;
+    Clear();
+  }
+}
+
+size_t BlockMeanCalculator::SamplesSinceLastUpdate() const {

[peah-webrtc, 2016/03/24 07:18:41]

To me the usage of this method requires a lot of understanding of the class
internals to be able to use. I.e., you need to know that
1) The class produces a new mean in a periodic manner.
2) You need to know that it resets the counter for the number of values added
when the new mean is produced.

Is there another way to do this that would be better? What about 
bool BlockMeanCalculator::NewMeanAvailable() const?

[minyue-webrtc, 2016/03/24 09:13:58]

Per offline discussion, we think if it better to use EndOfBlock()

+  return count_;
+}
+
+float BlockMeanCalculator::GetLatestMean() const {
+  return mean_;
+}
+
+// Flush all samples added.
+void BlockMeanCalculator::Clear() {
+  count_ = 0;
+  sum_ = 0.0;
+}
+
+}  // namespace webrtc