xxhash64_specialized.cpp

// 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);
}