Non-table based implementations of crc16 and crc8-maxim

test_crc.py

import crcmod.predefined

def _crc16(crc, c):
    crc ^= ord(c)
    for i in range(8):
        if crc & 0x1:
            crc = (crc >> 1) ^ 0xA001
        else:
            crc = (crc >> 1)
    return crc

def crc16(s):
    crc = 0
    for c in s:
        crc = _crc16(crc,c)
    return crc

def _crc8maxim(crc, c):
    crc ^= ord(c)
    for i in range(8):
        if crc & 0x1:
            crc = (crc >> 1) ^ 0x8C
        else:
            crc = (crc >> 1)
    return crc

def crc8maxim(s):
    crc = 0
    for c in s:
        crc = _crc8maxim(crc,c)
    return crc


if __name__ == "__main__":

    S = 'test124'

    print "CRC16 (%s)" % S
    crc = crcmod.predefined.Crc('crc-16')
    crc.update(S)
    print hex(crc.crcValue), 'vs', hex(crc16(S))

    print "CRC8 (%s)" % S
    crc = crcmod.predefined.Crc('crc-8-maxim')
    crc.update(S)
    print hex(crc.crcValue), 'vs', hex(crc8maxim(S))