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// 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), 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
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