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Reedbeta/xxhash64_specialized.cpp

Created May 11, 2023 20:29
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  1. Reedbeta created this gist May 11, 2023.
    35 changes: 35 additions & 0 deletions xxhash64_specialized.cpp
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    Original file line number Diff line number Diff line change
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    // Derived from: https://github.com/Cyan4973/xxHash
    // Specialized version of XXH64 for 64-bit inputs

    constexpr uint64_t XXH_PRIME64_1 = 0x9E3779B185EBCA87ULL;
    constexpr uint64_t XXH_PRIME64_2 = 0xC2B2AE3D27D4EB4FULL;
    constexpr uint64_t XXH_PRIME64_3 = 0x165667B19E3779F9ULL;
    constexpr uint64_t XXH_PRIME64_4 = 0x85EBCA77C2B2AE63ULL;
    constexpr uint64_t XXH_PRIME64_5 = 0x27D4EB2F165667C5ULL;

    inline uint64_t XXH64_round(uint64_t acc, uint64_t input)
    {
    acc += input * XXH_PRIME64_2;
    acc = std::rotl(acc, 31);
    acc *= XXH_PRIME64_1;
    return acc;
    }

    inline uint64_t XXH64_avalanche(uint64_t h64)
    {
    h64 ^= h64 >> 33;
    h64 *= XXH_PRIME64_2;
    h64 ^= h64 >> 29;
    h64 *= XXH_PRIME64_3;
    h64 ^= h64 >> 32;
    return h64;
    }

    inline uint64_t XXH64(uint64_t input, uint64_t seed = 0)
    {
    uint64_t h64 = seed + XXH_PRIME64_5 + 8;
    uint64_t const k1 = XXH64_round(0, input);
    h64 ^= k1;
    h64 = std::rotl(h64, 27) * XXH_PRIME64_1 + XXH_PRIME64_4;
    return XXH64_avalanche(h64);
    }