Murmur3 32-bit hash

murmur3_32.c

u32 murmur3_32_hash(void* data, size_t len) {
    u8* bytes = (u8*)data;
    i32 nblocks = len / 4;
    u32 h1 = 0x87c263d1;  // seed
    u32* blocks = (u32*)(bytes + nblocks * 4);

    for (i32 i = -nblocks; i; i++) {
        u32 k1 = blocks[i];
        k1 *= 0xcc9e2d51;
        k1 = (k1 << 15) | (k1 >> 17);
        k1 *= 0x1b873593;
        h1 ^= k1;
        h1 = (h1 << 13) | (h1 >> 19);
        h1 = h1 * 5 + 0xe6546b64;
    }

    u8* tail = bytes + nblocks * 4;
    u32 k1 = 0;

    switch (len & 3) {
        case 3:
            k1 ^= tail[2] << 16;
        case 2:
            k1 ^= tail[1] << 8;
        case 1:
            k1 ^= tail[0];
            k1 *= 0xcc9e2d51;
            k1 = (k1 << 15) | (k1 >> 17);
            k1 *= 0x1b873593;
            h1 ^= k1;
    };

    h1 ^= len;
    h1 ^= h1 >> 16;
    h1 *= 0x85ebca6b;
    h1 ^= h1 >> 13;
    h1 *= 0xc2b2ae35;
    h1 ^= h1 >> 16;

    return h1;
}