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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), 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());
}
std::pair<base::TimeDelta, base::TimeDelta> MovingAverage::GetMinAndMax() {
std::pair<base::TimeDelta, base::TimeDelta> result(samples_[0], samples_[0]);
const uint64_t size = std::min(static_cast<uint64_t>(depth_), count_);
for (uint64_t i = 1; i < size; i++) {
if (samples_[i] < result.first)
result.first = samples_[i];
if (samples_[i] > result.second)
result.second = samples_[i];
}
return result;
}
} // namespace media
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