MovingWindowAverageFast.h

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// Copyright Epic Games, Inc. All Rights Reserved.
#pragma once
#include "CoreMinimal.h"
#include "Containers/StaticArray.h"
 
/**
 * This class calculates a moving window average. Its designed to be used with floats or doubles and
 * keeps track of the average with every value pushed so is ideal when there is a one to one or one to many relationship
 * between calls to PushValue() and GetMovingWindowAverage() respectively.
 */
template <typename T, int32 ArraySize>
class FMovingWindowAverageFast
{
public:
    FMovingWindowAverageFast()
        : TotalValues(static_cast<T>(0))
        , AverageValue(static_cast<T>(0))
        , RemoveNextIdx(0)
        , NumValuesUsed(0)
    {
        static_assert(ArraySize > 0, "ArraySize must be greater than zero");
    }
 
    void PushValue(T Value)
    {
        T ValueRemoved = static_cast<T>(0);
 
        const T NumItemsPrev = static_cast<T>(NumValuesUsed);
 
        if (ArraySize == NumValuesUsed)
        {
            ValueRemoved = ValuesArray[RemoveNextIdx];
            ValuesArray[RemoveNextIdx] = Value;
            RemoveNextIdx = (RemoveNextIdx + 1) % ArraySize;
        }
        else
        {
            ValuesArray[NumValuesUsed] = Value;
            ++NumValuesUsed;
        }
 
        const T MovingWindowItemsNumCur = static_cast<T>(NumValuesUsed);
        TotalValues = TotalValues - ValueRemoved + Value;
        AverageValue = TotalValues / MovingWindowItemsNumCur;
    }
 
    T GetAverage() const
    {
        return AverageValue;
    }
 
private:
    TStaticArray<T, ArraySize> ValuesArray;
 
    T TotalValues;
    T AverageValue;
 
    /** The array Index of the next item to remove when the moving window is full */
    int32 RemoveNextIdx;
    int32 NumValuesUsed;
};