CRC.py

from linecache import updatecache


crc_lookup_table = [
          0x0000,0x1189,0x2312,0x329b,0x4624,0x57ad,0x6536,0x74bf,
          0x8c48,0x9dc1,0xaf5a,0xbed3,0xca6c,0xdbe5,0xe97e,0xf8f7,
          0x1081,0x0108,0x3393,0x221a,0x56a5,0x472c,0x75b7,0x643e,
          0x9cc9,0x8d40,0xbfdb,0xae52,0xdaed,0xcb64,0xf9ff,0xe876,
          0x2102,0x308b,0x0210,0x1399,0x6726,0x76af,0x4434,0x55bd,
          0xad4a,0xbcc3,0x8e58,0x9fd1,0xeb6e,0xfae7,0xc87c,0xd9f5,
          0x3183,0x200a,0x1291,0x0318,0x77a7,0x662e,0x54b5,0x453c,
          0xbdcb,0xac42,0x9ed9,0x8f50,0xfbef,0xea66,0xd8fd,0xc974,
          0x4204,0x538d,0x6116,0x709f,0x0420,0x15a9,0x2732,0x36bb,
          0xce4c,0xdfc5,0xed5e,0xfcd7,0x8868,0x99e1,0xab7a,0xbaf3,
          0x5285,0x430c,0x7197,0x601e,0x14a1,0x0528,0x37b3,0x263a,
          0xdecd,0xcf44,0xfddf,0xec56,0x98e9,0x8960,0xbbfb,0xaa72,
          0x6306,0x728f,0x4014,0x519d,0x2522,0x34ab,0x0630,0x17b9,
          0xef4e,0xfec7,0xcc5c,0xddd5,0xa96a,0xb8e3,0x8a78,0x9bf1,
          0x7387,0x620e,0x5095,0x411c,0x35a3,0x242a,0x16b1,0x0738,
          0xffcf,0xee46,0xdcdd,0xcd54,0xb9eb,0xa862,0x9af9,0x8b70,
          0x8408,0x9581,0xa71a,0xb693,0xc22c,0xd3a5,0xe13e,0xf0b7,
          0x0840,0x19c9,0x2b52,0x3adb,0x4e64,0x5fed,0x6d76,0x7cff,
          0x9489,0x8500,0xb79b,0xa612,0xd2ad,0xc324,0xf1bf,0xe036,
          0x18c1,0x0948,0x3bd3,0x2a5a,0x5ee5,0x4f6c,0x7df7,0x6c7e,
          0xa50a,0xb483,0x8618,0x9791,0xe32e,0xf2a7,0xc03c,0xd1b5,
          0x2942,0x38cb,0x0a50,0x1bd9,0x6f66,0x7eef,0x4c74,0x5dfd,
          0xb58b,0xa402,0x9699,0x8710,0xf3af,0xe226,0xd0bd,0xc134,
          0x39c3,0x284a,0x1ad1,0x0b58,0x7fe7,0x6e6e,0x5cf5,0x4d7c,
          0xc60c,0xd785,0xe51e,0xf497,0x8028,0x91a1,0xa33a,0xb2b3,
          0x4a44,0x5bcd,0x6956,0x78df,0x0c60,0x1de9,0x2f72,0x3efb,
          0xd68d,0xc704,0xf59f,0xe416,0x90a9,0x8120,0xb3bb,0xa232,
          0x5ac5,0x4b4c,0x79d7,0x685e,0x1ce1,0x0d68,0x3ff3,0x2e7a,
          0xe70e,0xf687,0xc41c,0xd595,0xa12a,0xb0a3,0x8238,0x93b1,
          0x6b46,0x7acf,0x4854,0x59dd,0x2d62,0x3ceb,0x0e70,0x1ff9,
          0xf78f,0xe606,0xd49d,0xc514,0xb1ab,0xa022,0x92b9,0x8330,
          0x7bc7,0x6a4e,0x58d5,0x495c,0x3de3,0x2c6a,0x1ef1,0x0f78
]

def UpdateCRC(crc, newByte):
    index = (crc ^ newByte) & 0xff  
    table_value = crc_lookup_table[index]
    retval = (crc >> 8) ^ table_value
    return retval


def CheckCRC(buffer, start, len, crc):
    c_crc = 0
    index = start

    if len < 8:
        return False

    for i in range(0, 6):
        c_crc = UpdateCRC(c_crc, buffer[index])
        index+=1
    index+=1
    index+=1
    
    for i in range(8, len):
        c_crc = UpdateCRC(c_crc, buffer[index])
        index+=1

    return (c_crc == crc)