| // 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 "media/base/moving_average.h" |
| |
| #include <algorithm> |
| |
| namespace media { |
| |
| MovingAverage::MovingAverage(size_t depth) : depth_(depth), samples_(depth_) {} |
| |
| MovingAverage::~MovingAverage() = default; |
| |
| 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; |
| oldest = sample; |
| if (sample > max_) |
| max_ = 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 base::TimeDelta average = Average(); |
| const uint64_t size = std::min(static_cast<uint64_t>(depth_), count_); |
| |
| // Perform the calculation in floating point since squaring the delta can |
| // exceed the bounds of a uint64_t value given two int64_t inputs. |
| double deviation_secs = 0; |
| for (uint64_t i = 0; i < size; ++i) { |
| const double x = (samples_[i] - average).InSecondsF(); |
| deviation_secs += x * x; |
| } |
| |
| deviation_secs /= size; |
| return base::TimeDelta::FromSecondsD(std::sqrt(deviation_secs)); |
| } |
| |
| void MovingAverage::Reset() { |
| count_ = 0; |
| total_ = base::TimeDelta(); |
| max_ = kNoTimestamp; |
| std::fill(samples_.begin(), samples_.end(), base::TimeDelta()); |
| } |
| |
| } // namespace media |