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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* Calculate the rolling mean of a series of values. */
#ifndef mozilla_RollingMean_h_
#define mozilla_RollingMean_h_
#include "mozilla/Assertions.h"
#include "mozilla/Vector.h"
#include <stddef.h>
#include <type_traits>
namespace mozilla {
/**
* RollingMean<T> calculates a rolling mean of the values it is given. It
* accumulates the total as values are added and removed. The second type
* argument S specifies the type of the total. This may need to be a bigger
* type in order to maintain that the sum of all values in the average doesn't
* exceed the maximum input value.
*
* WARNING: Float types are not supported due to rounding errors.
*/
template <typename T, typename S>
class RollingMean {
private:
size_t mInsertIndex;
size_t mMaxValues;
Vector<T> mValues;
S mTotal;
public:
static_assert(!std::is_floating_point_v<T>,
"floating-point types are unsupported due to rounding "
"errors");
explicit RollingMean(size_t aMaxValues)
: mInsertIndex(0), mMaxValues(aMaxValues), mTotal(0) {
MOZ_ASSERT(aMaxValues > 0);
}
RollingMean& operator=(RollingMean&& aOther) = default;
/**
* Insert a value into the rolling mean.
*/
bool insert(T aValue) {
MOZ_ASSERT(mValues.length() <= mMaxValues);
if (mValues.length() == mMaxValues) {
mTotal = mTotal - mValues[mInsertIndex] + aValue;
mValues[mInsertIndex] = aValue;
} else {
if (!mValues.append(aValue)) {
return false;
}
mTotal = mTotal + aValue;
}
mInsertIndex = (mInsertIndex + 1) % mMaxValues;
return true;
}
/**
* Calculate the rolling mean.
*/
T mean() const {
MOZ_ASSERT(!empty());
return T(mTotal / int64_t(mValues.length()));
}
bool empty() const { return mValues.empty(); }
/**
* Remove all values from the rolling mean.
*/
void clear() {
mValues.clear();
mInsertIndex = 0;
mTotal = T(0);
}
size_t maxValues() const { return mMaxValues; }
};
} // namespace mozilla
#endif // mozilla_RollingMean_h_
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