code: def crc16jit(buf, offset, crc, length):
    
    for index in range(offset, offset + length):
      data = buf[index]
      lookup = crc16_tab[((nb.u2(crc) >> 8) & nb.u2(0xFF)) ^ (data & nb.u2(0xFF))]
      crc = ((nb.u2(crc) << nb.u2(8)) & nb.u2(0xFFFF)) ^ lookup
      crc = nb.u2(crc) & nb.u2(0xFFFF)
    return crc
docs: CRC16 implementation acording to CCITT standards.