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