algds/src/mmhash.c

#include "mmhash.h"

/*-----------------------------------------------------------------------------
// MurmurHash2, 64-bit versions, by Austin Appleby
//
// The same caveats as 32-bit MurmurHash2 apply here - beware of alignment
// and endian-ness issues if used across multiple platforms.
//
// 64-bit hash for 64-bit platforms
*/

uint64_t mmhash(const void *key, int len, uint64_t seed) {
    const uint64_t m = 0xc6a4a7935bd1e995LL;
    const int r = 47;

    uint64_t h = seed ^ (len * m);

    const uint64_t *data = (const uint64_t *)key;
    const uint64_t *end = data + (len / 8);

    while (data != end) {
        uint64_t k = *data++;

        k *= m;
        k ^= k >> r;
        k *= m;

        h ^= k;
        h *= m;
    }

    const unsigned char *data2 = (const unsigned char *)data;

    switch (len & 7) {
        case 7:
            h ^= ((uint64_t)data2[6]) << 48;
        case 6:
            h ^= ((uint64_t)data2[5]) << 40;
        case 5:
            h ^= ((uint64_t)data2[4]) << 32;
        case 4:
            h ^= ((uint64_t)data2[3]) << 24;
        case 3:
            h ^= ((uint64_t)data2[2]) << 16;
        case 2:
            h ^= ((uint64_t)data2[1]) << 8;
        case 1:
            h ^= ((uint64_t)data2[0]);
            h *= m;
    };

    h ^= h >> r;
    h *= m;
    h ^= h >> r;

    return h;
}