CRC_BITS
ret = add_bits(p, crc, CRC_BITS);
ret = next_bits(&p, &crc, CRC_BITS);
msgpoly ^= (unsigned long)crc << (8*len - CRC_BITS);
msgpoly ^= crc >> (CRC_BITS - 8*len);
return msgpoly ^ ((unsigned long)crc << (BITS_PER_LONG - CRC_BITS));