BuzHash.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "Memory/MemoryView.h"
 
struct FBuzHash
{
public:
    UE_FORCEINLINE_HINT void Reset() { *this = FBuzHash(); }
 
    UE_FORCEINLINE_HINT uint32 Get() const { return State; }
 
    UE_FORCEINLINE_HINT uint64 GetWindowSize() const { return Count; }
 
    inline void Add(uint8 X)
    {
        State = Rol32(State, 1) ^ Table[X];
        Count++;
    }
 
    UE_FORCEINLINE_HINT void Add(FMemoryView View)
    {
        Add((const uint8*)View.GetData(), View.GetSize());
    }
 
    inline void Add(const uint8* Data, uint64 Size)
    {
        for (uint64 Idx = 0; Idx < Size; ++Idx)
        {
            Add(Data[Idx]);
        }
    }
 
    inline void Sub(uint8 X)
    {
        State = State ^ Rol32(Table[X], uint32(Count - 1));
        Count--;
    }
 
private:
    CORE_API static const uint32 Table[256];
 
    uint64 Count = 0;
    uint32 State = 0;
 
    static inline uint32 Rol32(uint32 V, uint32 N)
    {
        N &= 31;
        return ((V) << (N)) | ((V) >> (32 - N));
    }
};