checkbits
if (si->checkbits) {
unsigned checkbits:1;
checkbits(in, off, sizeof(smallbits), 0);
checkbits(ou, off, sizeof(smallbits), 0);
checkbits(ex, off, sizeof(smallbits), 0);
checkbits(in, off, ni, nd);
checkbits(ou, off, ni, nd);
checkbits(ex, off, ni, nd);