kinda hash or crc

hashing-experiment.c

   if (sizeof(uintmax_t) == 8) {
        size_t i;
        uintmax_t
            *l = (uintmax_t *) str->str,
            xx = 0x2020202020202020ULL;
        ;
        for (i=0; i < str->len / 8; i++) {
            xx ^= l[i];
        }
        unsigned char x =
            (( xx & 0xff00000000000000ULL ) >> 56) ^
            (( xx & 0x00ff000000000000ULL ) >> 48) ^
            (( xx & 0x0000ff0000000000ULL ) >> 40) ^
            (( xx & 0x000000ff00000000ULL ) >> 32) ^
            (( xx & 0x00000000ff000000ULL ) >> 24) ^
            (( xx & 0x0000000000ff0000ULL ) >> 16) ^
            (( xx & 0x000000000000ff00ULL ) >>  8) ^
            (( xx & 0x00000000000000ffULL ) >>  0)
        ;
        i *= 8;
        for (; i < str->len; i++) {
            x ^= str->str[i];
        }
        return x;