BuildPatchHash.h

Go to the documentation of this file.

// Copyright Epic Games, Inc. All Rights Reserved.
#pragma once
 
#include "CoreMinimal.h"
#include "Core/RingBuffer.h"
 
/*=============================================================================
    BuildPatchHash.h: Declares and implements template classes for use with the 
    Build and Patching hash functionality.
=============================================================================*/
 
#define ROTLEFT_64B( Value, Shifts ) Value = ( ( ( Value ) << ( ( Shifts ) % 64 ) ) | ( ( Value ) >> ( ( 64 - ( ( Shifts ) % 64 ) ) % 64 ) ) )
 
struct FRollingHashConst
{
    // The lookup hash table
    static uint64 HashTable[ 256 ];
    
    static void Init();
};
 
class FRollingHash
{
    // A typedef for our data ring buffer
    typedef TRingBuffer< uint8 > HashRingBuffer;
 
public:
    FRollingHash(uint32 WindowSize);
 
    void ConsumeByte( const uint8& NewByte );
 
    void ConsumeBytes( const uint8* NewBytes, const uint32& NumBytes );
 
    void RollForward( const uint8& NewByte );
 
    void Clear();
 
    const uint64 GetWindowHash() const;
 
    const HashRingBuffer& GetWindowData() const;
 
    const uint32 GetNumDataNeeded() const;
 
    const uint32 GetWindowSize() const;
 
    static uint64 GetHashForDataSet( const uint8* DataSet, uint32 WindowSize );
 
private:
    FRollingHash();
    // The data size that we roll over.
    const uint32 WindowSize = 0;
    // The current hash value
    uint64 HashState = 0;
    // The number of bytes we have consumed so far, used in hash function and to check validity of calls
    uint32 NumBytesConsumed = 0;
    // Store the data to make access and rolling easier
    HashRingBuffer WindowData = 0;
};
 
static bool CheckRollingHashAlgorithm()
{
    bool bCheckOk = true;
    // Sanity Check the RollingHash code!!
    FString IndivWords[6];
    IndivWords[0] = "123456";   IndivWords[1] = "7890-=";   IndivWords[2] = "qwerty";   IndivWords[3] = "uiop[]";   IndivWords[4] = "asdfgh";   IndivWords[5] = "jkl;'#";
    FString DataToRollOver = FString::Printf( TEXT( "%s%s%s%s%s%s" ), *IndivWords[0], *IndivWords[1], *IndivWords[2], *IndivWords[3], *IndivWords[4], *IndivWords[5] );
    uint64 IndivHashes[6];
    for (uint32 idx = 0; idx < 6; ++idx )
    {
        uint8 Converted[6];
        for (uint32 iChar = 0; iChar < 6; ++iChar )
            Converted[iChar] = IndivWords[idx][iChar];
        IndivHashes[idx] = FRollingHash::GetHashForDataSet( Converted, 6 );
    }
 
    FRollingHash RollingHash(6);
    uint32 StrIdx = 0;
    for (uint32 k=0; k<6; ++k)
        RollingHash.ConsumeByte( DataToRollOver[ StrIdx++ ] );
    bCheckOk = bCheckOk && IndivHashes[0] == RollingHash.GetWindowHash();
    for (uint32 k=0; k<6; ++k)
        RollingHash.RollForward( DataToRollOver[ StrIdx++ ] );
    bCheckOk = bCheckOk && IndivHashes[1] == RollingHash.GetWindowHash();
    for (uint32 k=0; k<6; ++k)
        RollingHash.RollForward( DataToRollOver[ StrIdx++ ] );
    bCheckOk = bCheckOk && IndivHashes[2] == RollingHash.GetWindowHash();
    for (uint32 k=0; k<6; ++k)
        RollingHash.RollForward( DataToRollOver[ StrIdx++ ] );
    bCheckOk = bCheckOk && IndivHashes[3] == RollingHash.GetWindowHash();
    for (uint32 k=0; k<6; ++k)
        RollingHash.RollForward( DataToRollOver[ StrIdx++ ] );
    bCheckOk = bCheckOk && IndivHashes[4] == RollingHash.GetWindowHash();
    for (uint32 k=0; k<6; ++k)
        RollingHash.RollForward( DataToRollOver[ StrIdx++ ] );
    bCheckOk = bCheckOk && IndivHashes[5] == RollingHash.GetWindowHash();
 
    return bCheckOk;
}