crc16 computer

crc16.py

################# Compute CRC16 from buffer ###############
""" usage:  add : from crc16 import crc16
            call crc16(vCRCList)
"""
def crc16(packet):

    POLY = 0x8408                   # 0x8408 is deduced from the polynomial X**16 + X**12 + X**5 + X**0

    # process each byte
    vFCS = 0xFFFF;                  # init FCS to all ones
    for byte in packet:
        vFCS ^= ord(byte)           # attention au XOR...
        # process each bit of the current byte
        for x in range(8):
            if (vFCS & 1):
                vFCS = (vFCS>>1) ^ POLY;
            else:
                vFCS >>= 1;

    vFCS ^= 0xFFFF;                 # finally invert vFCS
    #print "\nvFCS final = %x" % (vFCS)
    return vFCS

if __name__ == '__main__':
    vFrm = ['\x00', '\x00', '\x00', '\x80']
    calccrc = crc16(vFrm)        #send frame to function (without the crc!)
    print "calccrc %x" % calccrc