Adding BlockMeanCalculator for AEC.

webrtc/modules/audio_processing/utility/mean_calculator.h

+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_PROCESSING_UTILITY_MEAN_CALCULATOR_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_UTILITY_MEAN_CALCULATOR_H_
+
+#include <stddef.h>
+
+#include "webrtc/base/constructormagic.h"
+
+namespace webrtc {
+
+// MeanCalculator calculates the mean of a block of samples. Samples are added

[minyue-webrtc, 2016/03/21 15:27:52]

This should be called BlockMeanCalculator. I will not forget it.

+// one after another, and the mean is updated at the end of every block.
+class BlockMeanCalculator {
+ public:
+  explicit BlockMeanCalculator(size_t block_length);
+
+  // Reset.
+  void Reset();
+
+  // Add one sample to the sequence.
+  void AddSample(float sample);
+
+  // Return the number of newly added samples since latest update on mean value.
+  size_t SamplesSinceLastUpdate() const;
+
+  // Return the latest mean value.
+  float GetLatestMean() const;
+
+ private:
+  // Clear all samples added.
+  void Clear();
+
+  const size_t block_length_;
+  size_t count_;
+  float sum_;
+  float mean_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(BlockMeanCalculator);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_UTILITY_MEAN_CALCULATOR_H_