Faster version of the djb2 hash by making gcc recognize it is deterministic

faster-djb2-hash.c

uint32_t djb_hash(const char * const key, size_t keylen)
{
    uint32_t j = (uint32_t) 5381U;
    const unsigned char *ukey = (const unsigned char *) key;
    size_t i = (size_t) 0U;
    if (keylen >= (size_t) 8U) {
        const size_t keylen_chunk = keylen - 8U;
        while (i <= keylen_chunk) {
            const unsigned char * const p = ukey + i;
            i += (size_t) 8U;
            j = j * 33U ^ p[0]; j = j * 33U ^ p[1];
            j = j * 33U ^ p[2]; j = j * 33U ^ p[3];
            j = j * 33U ^ p[4]; j = j * 33U ^ p[5];
            j = j * 33U ^ p[6]; j = j * 33U ^ p[7];
        }
    }
    while (i < keylen) {
        j = j * 33U ^ ukey[i++];
    }    
    j &= 0xffffffff;
    
    return j;
}

j &= 0xffffffff is stripped out by the compiler if uint32_t is an exact 32-bit type as it should, and not a larger typedef'd type. It's only here for pure paranoia.