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// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/performance_manager/persistence/site_data/exponential_moving_average.h"
#include <cmath>
#include "base/check.h"
namespace performance_manager {
ExponentialMovingAverage::ExponentialMovingAverage(float alpha)
: alpha_(alpha) {
DCHECK(alpha_ > 0.0 && alpha_ < 1.0);
}
void ExponentialMovingAverage::AppendDatum(float datum) {
if (num_datums_ == 0) {
first_datum_ = datum;
value_ = datum;
} else {
value_ = value_ * (1.0 - alpha_) + datum * alpha_;
}
++num_datums_;
}
void ExponentialMovingAverage::PrependDatum(float datum) {
if (num_datums_ == 0) {
first_datum_ = datum;
value_ = datum;
} else {
// Back the previous first datum out of the value.
float beta = 1.0 - alpha_;
float betan = std::pow(1.0 - alpha_, num_datums_ - 1);
float first_datum_contrib = first_datum_ * betan;
float other_datums_contrib = value_ - first_datum_contrib;
first_datum_ = datum;
value_ = datum * betan * beta + first_datum_contrib * alpha_ +
other_datums_contrib;
}
++num_datums_;
}
void ExponentialMovingAverage::Clear() {
first_datum_ = 0.0;
value_ = 0.0;
num_datums_ = 0;
}
} // namespace performance_manager
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