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) {

[peah-webrtc, 2016/03/24 11:21:58]

You should add a DCHECK on the block_length not being zero.

[minyue-webrtc, 2016/03/24 11:43:33]

Done.

+}
+
+void BlockMeanCalculator::Reset() {
+  Clear();
+  mean_ = 0.0;
+}
+
+void BlockMeanCalculator::AddValue(float value) {
+  sum_ += value;
+  ++count_;
+  if (count_ == block_length_) {
+    mean_ = sum_ / block_length_;

[peah-webrtc, 2016/03/24 11:21:58]

You should add a DCHECK on the block_length not being zero.

[minyue-webrtc, 2016/03/24 11:43:33]

since block_length_ is qualified const, it is enough to check in ctor, I think.

+    Clear();
+  }
+}
+
+bool BlockMeanCalculator::EndOfBlock() const {

[peah-webrtc, 2016/03/24 11:21:58]

Another suggestion instead of "EndOfBlock" could be "FullBlockCollected". What
do you think of that? I think that is a bit more clear.

[minyue-webrtc, 2016/03/24 11:43:33]

I prefer EndOfBlock. Let's consider what people would expect when adding another
value after a whole block.

Naturally, EndOfBlock should return false, since the new added value does not
end a block.

But it is not obvious that FullBlockCollected should return false, since one may
argue that a full block has been collected.

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