static void inc_128(DRBG_CTR_CTX *cctx)
{
    int i;
    unsigned char c;
    unsigned char *p = &cctx->V[15];

    for (i = 0; i < 16; i++, p--) {
        c = *p;
        c++;
        *p = c;
        if (c != 0) {
            /* If we didn't wrap around, we're done. */
            break;
        }
    }
}