Function GenerateHash

SampleFramework12/v1.00/MurmurHash.cpp:76–151

//-----------------------------------------------------------------------------

Hash GenerateHash(const void* key, const int len, const uint32_t seed)
{
    const uint8_t * data = (const uint8_t*)key;
    const int nblocks = len / 16;

    uint64_t h1 = seed;
    uint64_t h2 = seed;

    const uint64_t c1 = BIG_CONSTANT(0x87c37b91114253d5);
    const uint64_t c2 = BIG_CONSTANT(0x4cf5ad432745937f);

    //----------
    // body

    const uint64_t * blocks = (const uint64_t *)(data);

    for(int i = 0; i < nblocks; i++)
    {
        uint64_t k1 = getblock(blocks,i*2+0);
        uint64_t k2 = getblock(blocks,i*2+1);

        k1 *= c1; k1  = ROTL64(k1,31); k1 *= c2; h1 ^= k1;

        h1 = ROTL64(h1,27); h1 += h2; h1 = h1*5+0x52dce729;

        k2 *= c2; k2  = ROTL64(k2,33); k2 *= c1; h2 ^= k2;

        h2 = ROTL64(h2,31); h2 += h1; h2 = h2*5+0x38495ab5;
    }

    //----------
    // tail

    const uint8_t * tail = (const uint8_t*)(data + nblocks*16);

    uint64_t k1 = 0;
    uint64_t k2 = 0;

    switch(len & 15)
    {
    case 15: k2 ^= uint64_t(tail[14]) << 48;
    case 14: k2 ^= uint64_t(tail[13]) << 40;
    case 13: k2 ^= uint64_t(tail[12]) << 32;
    case 12: k2 ^= uint64_t(tail[11]) << 24;
    case 11: k2 ^= uint64_t(tail[10]) << 16;
    case 10: k2 ^= uint64_t(tail[ 9]) << 8;
    case  9: k2 ^= uint64_t(tail[ 8]) << 0;
        k2 *= c2; k2  = ROTL64(k2,33); k2 *= c1; h2 ^= k2;

    case  8: k1 ^= uint64_t(tail[ 7]) << 56;
    case  7: k1 ^= uint64_t(tail[ 6]) << 48;
    case  6: k1 ^= uint64_t(tail[ 5]) << 40;
    case  5: k1 ^= uint64_t(tail[ 4]) << 32;
    case  4: k1 ^= uint64_t(tail[ 3]) << 24;
    case  3: k1 ^= uint64_t(tail[ 2]) << 16;
    case  2: k1 ^= uint64_t(tail[ 1]) << 8;
    case  1: k1 ^= uint64_t(tail[ 0]) << 0;
        k1 *= c1; k1  = ROTL64(k1,31); k1 *= c2; h1 ^= k1;