CRC-CCITT 16-bit Python Manual Calculation

Question

Problem

I am writing code for an embedded device. A lot of solutions out there for CRC-CCITT 16-bit calculations require libraries.

Given that u

Answer 1

The accepted answer above is wrong. It does not augment a zero-length input with 16 bits of 0, as given by http://srecord.sourceforge.net/crc16-ccitt.html. Luckily, it can be fixed very easily. I will only post the changes that I've made.

def crc(str):
    crc = PRESET
    # start crc with two zero bytes
    for _ in range(2):
        crc = _update_crc(crc, 0)
    for c in str:
        crc = _update_crc(crc, ord(c))
    return crc

def crcb(*i):
    crc = PRESET
    for _ in range(2):
        crc = _update_crc(crc, 0)
    for c in i:
        crc = _update_crc(crc, c)
    return crc

Now, if we compare the new implementation to the expected CRC values, we get the "good_crc" values instead of "bad_crc" values.