Refactor QualityScaler and MovingAverage

webrtc/modules/video_coding/utility/moving_average.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/video_coding/utility/moving_average.h"
+
+#include <algorithm>
+
+namespace webrtc {
+
+MovingAverage::MovingAverage(size_t s) : sum_history_(s + 1, 0) {}
+
+void MovingAverage::AddSample(int sample) {
+  count_++;
+  sum_ += sample;
+  sum_history_[count_ % sum_history_.size()] = sum_;
+}
+
+int MovingAverage::GetAverage() const {
+  return *GetAverage(size());
+}
+
+rtc::Optional<int> MovingAverage::GetAverage(size_t num_samples) const {
+  if (num_samples > size())
+    return rtc::Optional<int>();
+  if (num_samples == 0)
+    return rtc::Optional<int>(0);

[magjed_webrtc, 2016/09/07 11:55:16]

I find it more intuitive if we return rtc::Optional<int>() in the case
num_samples==0. You would need to change the return type of the the other
GetAverage() function for that change as well.

+  int sum = sum_ - sum_history_[(count_ - num_samples) % sum_history_.size()];
+  if (sum == 0)

[sakal, 2016/09/07 09:47:21]

What is this special case for? Looks like a bug to me.

[kthelgason, 2016/09/07 12:31:46]

Well spotted. That was left in by accident when I was making some changes.

+    sum = sum_;
+  return rtc::Optional<int>(sum / num_samples);
+}
+
+void MovingAverage::Reset() {
+  count_ = 0;
+  sum_ = 0;
+  std::fill(sum_history_.begin(), sum_history_.end(), 0);
+}
+
+size_t MovingAverage::size() const {
+  return std::min(count_, sum_history_.size() - 1);
+}
+
+}  // namespace webrtc