memcmp8.c

/*
attempt at writing a faster memcmp
*/
static iint_t INLINE memcmp8 (const char *as, const char* bs, iint_t len)
{
    uint64_t *a = (uint64_t*)as;
    uint64_t *b = (uint64_t*)bs;
    while (len > 8) {
        if (*a != *b) {
            return 1;
        }
        a++;
        b++;
        len -= 8;
    }

    uint64_t rem = len;

    uint64_t mask;
    switch (rem) {
        case 0: mask = 0x0000000000000000;
        break;
        case 1: mask = 0x00000000000000FF;
        break;
        case 2: mask = 0x000000000000FFFF;
        break;
        case 3: mask = 0x0000000000FFFFFF;
        break;
        case 4: mask = 0x00000000FFFFFFFF;
        break;
        case 5: mask = 0x000000FFFFFFFFFF;
        break;
        case 6: mask = 0x0000FFFFFFFFFFFF;
        break;
        case 7: mask = 0x00FFFFFFFFFFFFFF;
        break;
    }
    //mask = ~(mask >> ((7-rem)*8));
    //printf("%llx %llx %llx %lld\n", mask, *a & mask, *b & mask, len);

    if (((*a) & mask) != ((*b) & mask)) {
        return 1;
    }

    return 0;
}