TypeHash.h

Go to the documentation of this file.

// Copyright 1998-2017 Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "../BasicTypes.h"
#include "IsEnum.h"
#include "Tuple.h"
 
/**
 * Combines two hash values to get a third.
 * Note - this function is not commutative.
 */
inline uint32 HashCombine(uint32 A, uint32 C)
{
    uint32 B = 0x9e3779b9;
    A += B;
 
    A -= B; A -= C; A ^= (C>>13);
    B -= C; B -= A; B ^= (A<<8);
    C -= A; C -= B; C ^= (B>>13);
    A -= B; A -= C; A ^= (C>>12);
    B -= C; B -= A; B ^= (A<<16);
    C -= A; C -= B; C ^= (B>>5);
    A -= B; A -= C; A ^= (C>>3);
    B -= C; B -= A; B ^= (A<<10);
    C -= A; C -= B; C ^= (B>>15);
 
    return C;
}
 
 
inline uint32 PointerHash(const void* Key,uint32 C = 0)
{
    // Avoid LHS stalls on PS3 and Xbox 360
#if PLATFORM_64BITS
    // Ignoring the lower 4 bits since they are likely zero anyway.
    // Higher bits are more significant in 64 bit builds.
    auto PtrInt = reinterpret_cast<UPTRINT>(Key) >> 4;
#else
    auto PtrInt = reinterpret_cast<UPTRINT>(Key);
#endif
 
    return HashCombine(static_cast<uint32>(PtrInt), C);
}
 
 
//
// Hash functions for common types.
//
 
inline uint32 GetTypeHash( const uint8 A )
{
    return A;
}
 
inline uint32 GetTypeHash( const int8 A )
{
    return A;
}
 
inline uint32 GetTypeHash( const uint16 A )
{
    return A;
}
 
inline uint32 GetTypeHash( const int16 A )
{
    return A;
}
 
inline uint32 GetTypeHash( const int32 A )
{
    return A;
}
 
inline uint32 GetTypeHash( const uint32 A )
{
    return A;
}
 
inline uint32 GetTypeHash( const uint64 A )
{
    return (uint32)A+((uint32)(A>>32) * 23);
}
 
inline uint32 GetTypeHash( const int64 A )
{
    return (uint32)A+((uint32)(A>>32) * 23);
}
 
#if PLATFORM_MAC
inline uint32 GetTypeHash( const __uint128_t A )
{
    uint64 Low = (uint64)A;
    uint64 High = (uint64)(A >> 64);
    return GetTypeHash(Low) ^ GetTypeHash(High);
}
#endif
 
inline uint32 GetTypeHash( float Value )
{
    return *(uint32*)&Value;
}
 
inline uint32 GetTypeHash( double Value )
{
    return GetTypeHash(*(uint64*)&Value);
}
 
inline uint32 GetTypeHash( const void* A )
{
    return PointerHash(A);
}
 
inline uint32 GetTypeHash( void* A )
{
    return PointerHash(A);
}
 
template <typename EnumType>
FORCEINLINE  typename TEnableIf<TIsEnum<EnumType>::Value, uint32>::Type GetTypeHash(EnumType E)
{
    return GetTypeHash((__underlying_type(EnumType))E);
}
 
namespace UE4TypeHash_Private
{
    template <uint32 ArgToCombine, uint32 ArgCount>
    struct TGetTupleHashHelper
    {
        template <typename TupleType>
        FORCEINLINE static uint32 Do(uint32 Hash, const TupleType& Tuple)
        {
            return TGetTupleHashHelper<ArgToCombine + 1, ArgCount>::Do(HashCombine(Hash, GetTypeHash(Tuple.template Get<ArgToCombine>())), Tuple);
        }
    };
 
    template <uint32 ArgIndex>
    struct TGetTupleHashHelper<ArgIndex, ArgIndex>
    {
        template <typename TupleType>
        FORCEINLINE static uint32 Do(uint32 Hash, const TupleType& Tuple)
        {
            return Hash;
        }
    };
}
 
template <typename... Types>
FORCEINLINE uint32 GetTypeHash(const TTuple<Types...>& Tuple)
{
    return UE4TypeHash_Private::TGetTupleHashHelper<1u, sizeof...(Types)>::Do(GetTypeHash(Tuple.template Get<0>()), Tuple);
}
 
FORCEINLINE uint32 GetTypeHash(const TTuple<>& Tuple)
{
    return 0;
}