| // Copyright 2015 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "cobalt/media/base/moving_average.h" |
| |
| #include <algorithm> |
| |
| namespace cobalt { |
| namespace media { |
| |
| MovingAverage::MovingAverage(size_t depth) |
| : depth_(depth), count_(0), samples_(depth_), square_sum_us_(0) {} |
| |
| MovingAverage::~MovingAverage() {} |
| |
| void MovingAverage::AddSample(base::TimeDelta sample) { |
| // |samples_| is zero-initialized, so |oldest| is also zero before |count_| |
| // exceeds |depth_|. |
| base::TimeDelta& oldest = samples_[count_++ % depth_]; |
| total_ += sample - oldest; |
| square_sum_us_ += sample.InMicroseconds() * sample.InMicroseconds() - |
| oldest.InMicroseconds() * oldest.InMicroseconds(); |
| oldest = sample; |
| } |
| |
| base::TimeDelta MovingAverage::Average() const { |
| DCHECK_GT(count_, 0u); |
| |
| // TODO(dalecurtis): Consider limiting |depth| to powers of two so that we can |
| // replace the integer divide with a bit shift operation. |
| |
| return total_ / std::min(static_cast<uint64_t>(depth_), count_); |
| } |
| |
| base::TimeDelta MovingAverage::Deviation() const { |
| DCHECK_GT(count_, 0u); |
| |
| const double size = std::min(static_cast<uint64_t>(depth_), count_); |
| const double average_us = total_.InMicroseconds() / size; |
| double sqr_deviation_us = square_sum_us_ / size - average_us * average_us; |
| if (sqr_deviation_us < 0) sqr_deviation_us = 0; |
| |
| return base::TimeDelta::FromMicroseconds(sqrt(sqr_deviation_us)); |
| } |
| |
| void MovingAverage::Reset() { |
| count_ = 0; |
| total_ = base::TimeDelta(); |
| square_sum_us_ = 0; |
| std::fill(samples_.begin(), samples_.end(), base::TimeDelta()); |
| } |
| |
| } // namespace media |
| } // namespace cobalt |