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pythonmathbyteprotocolscrc

CRC doesn't return expected value

I have some technical documentation and try to replicate the given CRC algorithm in python. However I don't get the correct results. How do I have to tweak my algo to match the docs?

This is the documentation:

enter image description here

And this is my code:

data1 = b'\0x01\0x04\0x00\0x0b\0x00\0x01'
data2 = b'\0x01\0x03\0x00\0x65\0x00\0x01'


def crc16(data : bytearray):
    length = len(data)
    crc = 0xffff
    for i in range(0, length):
        crc ^= data[i]
        for j in range(0,8):
            if (crc & 0x01):
                crc =(crc >> 1) ^ 0xa001
            else:
                crc = crc >> 1
    return crc

print(crc16(data1).to_bytes(2, 'big'))
print(crc16(data2).to_bytes(2, 'big'))

Here are some examples for the documentation: enter image description here enter image description here

Here are my results:

b'\xc9Y'
b'\xd4\xd1'
Solution

  • Your input data is wrong. The first one should be b'\x01\x04\x00\x0b\x00\x01' for example. The first string as written by you has '\0' (a null character), followed by the literal characters 'x04', and so on. You can check this by printing the strings.

    Once this is corrected your code appears to give the correct results.

    As a minor note, your type information for the data parameter says it takes a bytearray but you're actually passing it bytes.