Gist to calculate CRC of an input polynomial in bit-string format using modulo-2-division

crc.py

def xor(a, b):

    # initialize result
    result = []

    # Traverse all bits, if bits are
    # same, then XOR is 0, else 1
    for i in range(1, len(b)):
        if a[i] == b[i]:
            result.append('0')
        else:
            result.append('1')

    return ''.join(result)


# Performs Modulo-2 division
def modulo_2_division(divident, divisor):
    itr = len(divisor)
    tmp = divident[0: itr]

    while itr < len(divident):

        if tmp[0] == '1':
            tmp = xor(divisor, tmp) + divident[itr]

        else:
            tmp = xor('0'*itr, tmp) + divident[itr]
        itr += 1
    if tmp[0] == '1':
        tmp = xor(divisor, tmp)
    else:
        tmp = xor('0'*itr, tmp)

    checkword = tmp
    return checkword


def encodeData(data, key):

    l_key = len(key)

    zero_appended_data = data + '0'*(l_key-1)
    remainder = modulo_2_division(zero_appended_data, key)

    codeword = data + remainder
    print("Input Data  : ", data)
    print("Remainder   : ", remainder)
    print("Encoded Data: ", codeword, f" = '{data}' + '{remainder}'")


# Driver code
data = ["11000010", "1010"]
key = ["100011101", "1101"]

for i in range(len(data)):
    print("------------------------------")
    print(f"Dataset {i+1}")
    print("------------------------------")
    encodeData(data[i], key[i])