1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/mfbt/RollingMean.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,109 @@
1.4 +/* -*- Mode: C++; tab-w idth: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
1.5 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.6 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.7 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.8 +
1.9 +/* A set abstraction for enumeration values. */
1.10 +
1.11 +#ifndef mozilla_RollingMean_h_
1.12 +#define mozilla_RollingMean_h_
1.13 +
1.14 +#include "mozilla/Assertions.h"
1.15 +#include "mozilla/TypeTraits.h"
1.16 +#include "mozilla/Vector.h"
1.17 +
1.18 +#include <algorithm>
1.19 +#include <stddef.h>
1.20 +#include <stdint.h>
1.21 +
1.22 +namespace mozilla {
1.23 +
1.24 +/**
1.25 + * RollingMean<T> calculates a rolling mean of the values it is given. It
1.26 + * accumulates the total as values are added and removed. The second type
1.27 + * argument S specifies the type of the total. This may need to be a bigger
1.28 + * type in order to maintain that the sum of all values in the average doesn't
1.29 + * exceed the maximum input value.
1.30 + *
1.31 + * WARNING: Float types are not supported due to rounding errors.
1.32 + */
1.33 +template<typename T, typename S>
1.34 +class RollingMean
1.35 +{
1.36 + private:
1.37 + size_t mInsertIndex;
1.38 + size_t mMaxValues;
1.39 + Vector<T> mValues;
1.40 + S mTotal;
1.41 +
1.42 + public:
1.43 + static_assert(!IsFloatingPoint<T>::value,
1.44 + "floating-point types are unsupported due to rounding "
1.45 + "errors");
1.46 +
1.47 + RollingMean(size_t aMaxValues)
1.48 + : mInsertIndex(0),
1.49 + mMaxValues(aMaxValues),
1.50 + mTotal(0)
1.51 + {
1.52 + MOZ_ASSERT(aMaxValues > 0);
1.53 + }
1.54 +
1.55 + RollingMean& operator=(RollingMean&& aOther) {
1.56 + MOZ_ASSERT(this != &aOther, "self-assignment is forbidden");
1.57 + this->~RollingMean();
1.58 + new(this) RollingMean(aOther.mMaxValues);
1.59 + mInsertIndex = aOther.mInsertIndex;
1.60 + mTotal = aOther.mTotal;
1.61 + mValues.swap(aOther.mValues);
1.62 + return *this;
1.63 + }
1.64 +
1.65 + /**
1.66 + * Insert a value into the rolling mean.
1.67 + */
1.68 + bool insert(T aValue) {
1.69 + MOZ_ASSERT(mValues.length() <= mMaxValues);
1.70 +
1.71 + if (mValues.length() == mMaxValues) {
1.72 + mTotal = mTotal - mValues[mInsertIndex] + aValue;
1.73 + mValues[mInsertIndex] = aValue;
1.74 + } else {
1.75 + if (!mValues.append(aValue))
1.76 + return false;
1.77 + mTotal = mTotal + aValue;
1.78 + }
1.79 +
1.80 + mInsertIndex = (mInsertIndex + 1) % mMaxValues;
1.81 + return true;
1.82 + }
1.83 +
1.84 + /**
1.85 + * Calculate the rolling mean.
1.86 + */
1.87 + T mean() {
1.88 + MOZ_ASSERT(!empty());
1.89 + return T(mTotal / mValues.length());
1.90 + }
1.91 +
1.92 + bool empty() {
1.93 + return mValues.empty();
1.94 + }
1.95 +
1.96 + /**
1.97 + * Remove all values from the rolling mean.
1.98 + */
1.99 + void clear() {
1.100 + mValues.clear();
1.101 + mInsertIndex = 0;
1.102 + mTotal = T(0);
1.103 + }
1.104 +
1.105 + size_t maxValues() {
1.106 + return mMaxValues;
1.107 + }
1.108 +};
1.109 +
1.110 +} // namespace mozilla
1.111 +
1.112 +#endif // mozilla_RollingMean_h_
