HashCombine.h

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// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT
 
#pragma once
 
JPH_NAMESPACE_BEGIN
 
inline uint64 HashBytes(const void *inData, uint inSize, uint64 inSeed = 0xcbf29ce484222325UL)
{
    uint64 hash = inSeed;
    for (const uint8 *data = reinterpret_cast<const uint8 *>(inData); data < reinterpret_cast<const uint8 *>(inData) + inSize; ++data)
    {
        hash = hash ^ uint64(*data);
        hash = hash * 0x100000001b3UL;
    }
    return hash;
}
 
inline uint64 Hash64(uint64 inValue)
{
    uint64 hash = inValue;
    hash = (~hash) + (hash << 21); // hash = (hash << 21) - hash - 1;
    hash = hash ^ (hash >> 24);
    hash = (hash + (hash << 3)) + (hash << 8); // hash * 265
    hash = hash ^ (hash >> 14);
    hash = (hash + (hash << 2)) + (hash << 4); // hash * 21
    hash = hash ^ (hash >> 28);
    hash = hash + (hash << 31);
    return hash;
}
 
template <typename T>
inline void HashCombineHelper(size_t &ioSeed, const T &inValue)
{
    std::hash<T> hasher;
    ioSeed ^= hasher(inValue) + 0x9e3779b9 + (ioSeed << 6) + (ioSeed >> 2);
}
 
template <typename... Values>
inline void HashCombine(std::size_t &ioSeed, Values... inValues) 
{
    // Hash all values together using a fold expression
    (HashCombineHelper(ioSeed, inValues), ...);
}
 
JPH_NAMESPACE_END
 
JPH_SUPPRESS_WARNING_PUSH
JPH_CLANG_SUPPRESS_WARNING("-Wc++98-compat-pedantic")
 
#define JPH_MAKE_HASH_STRUCT(type, name, ...)               \
    struct [[nodiscard]] name                               \
    {                                                       \
        std::size_t operator()(const type &t) const         \
        {                                                   \
            std::size_t ret = 0;                            \
            ::JPH::HashCombine(ret, __VA_ARGS__);           \
            return ret;                                     \
        }                                                   \
    };
 
#define JPH_MAKE_HASHABLE(type, ...)                        \
    JPH_SUPPRESS_WARNING_PUSH                               \
    JPH_SUPPRESS_WARNINGS                                   \
    namespace std                                           \
    {                                                       \
        template<>                                          \
        JPH_MAKE_HASH_STRUCT(type, hash<type>, __VA_ARGS__) \
    }                                                       \
    JPH_SUPPRESS_WARNING_POP
 
JPH_SUPPRESS_WARNING_POP