Implementation of crc16 (CRC-16-CCITT) in python

crc16.py

def crc16(data: bytes, poly=0x8408):
    '''
    CRC-16-CCITT Algorithm
    '''
    data = bytearray(data)
    crc = 0xFFFF
    for b in data:
        cur_byte = 0xFF & b
        for _ in range(0, 8):
            if (crc & 0x0001) ^ (cur_byte & 0x0001):
                crc = (crc >> 1) ^ poly
            else:
                crc >>= 1
            cur_byte >>= 1
    crc = (~crc & 0xFFFF)
    crc = (crc << 8) | ((crc >> 8) & 0xFF)
    
    return crc & 0xFFFF

def crc16(data): ''' CRC-16 (CCITT) implemented with a precomputed lookup table ''' table = [ 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7, 0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF, 0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6, 0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485, 0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D, 0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4, 0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC, 0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823, 0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B, 0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A, 0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49, 0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70, 0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78, 0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F, 0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E, 0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256, 0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D, 0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634, 0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB, 0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3, 0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A, 0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92, 0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9, 0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1, 0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8, 0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0 ] crc = 0xFFFF for byte in data: crc = (crc << 8) ^ table[(crc >> 8) ^ byte] crc &= 0xFFFF # important, crc must stay 16bits all the way through print(crc, '{:04X}'.format(crc)) return('{:04X}'.format(crc)) crc16(b'\x92')

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On Thu, 27 Apr 2023 at 17:44, TrajcheKrstev ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ 420B is returned by this particular variant of crc16 if you feed it with b'45377 So if you can figure out the connection between that & your list you're good to go. Unfortunately nothing obvious comes to mind. … <#m_-2639103623622540039_> Well converting it from binary to hexadecimal it’s 0x92 and according to https://crccalc.com/ that should return 420B for CRC-16-CCITT-FALSE. If that is a different one than the above code, how can i change the code for this variant that i need? — Reply to this email directly, view it on GitHub <https://gist.github.com/oysstu/68072c44c02879a2abf94ef350d1c7c6#gistcomment-4550183> or unsubscribe <https://github.com/notifications/unsubscribe-auth/AV562M27VG3QMPOCZ3JCZHDXDIPURBFKMF2HI4TJMJ2XIZLTSKBKK5TBNR2WLJDHNFZXJJDOMFWWLK3UNBZGKYLEL52HS4DFQKSXMYLMOVS2I5DSOVS2I3TBNVS3W5DIOJSWCZC7OBQXE5DJMNUXAYLOORPWCY3UNF3GS5DZVRZXKYTKMVRXIX3UPFYGLK2HNFZXIQ3PNVWWK3TUUZ2G64DJMNZZDAVEOR4XAZNEM5UXG5FFOZQWY5LFVAZTOMRWGU4DSOFHORZGSZ3HMVZKMY3SMVQXIZI> . You are receiving this email because you commented on the thread. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub> .

This also works def crc_16(data): crc=0xFFFF; POLYNOMIAL=0x1021 for c in data: crc=crc^(c<<8) for j in range(8): crc=(crc<<1)^POLYNOMIAL if crc & 0x8000 else crc<<1 crc = crc & 0xFFFF; crc='%.04X'%crc print('msg', data, ' crc', crc); return crc crc_16(b'\x92') On Thu, 27 Apr 2023 at 18:35, Kris Mclean ***@***.***> wrote:

…

def crc16(data): ''' CRC-16 (CCITT) implemented with a precomputed lookup table ''' table = [ 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7, 0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF, 0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6, 0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485, 0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D, 0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4, 0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC, 0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823, 0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B, 0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A, 0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49, 0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70, 0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78, 0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F, 0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E, 0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256, 0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D, 0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634, 0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB, 0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3, 0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A, 0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92, 0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9, 0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1, 0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8, 0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0 ] crc = 0xFFFF for byte in data: crc = (crc << 8) ^ table[(crc >> 8) ^ byte] crc &= 0xFFFF # important, crc must stay 16bits all the way through print(crc, '{:04X}'.format(crc)) return('{:04X}'.format(crc)) crc16(b'\x92') On Thu, 27 Apr 2023 at 17:44, TrajcheKrstev ***@***.***> wrote: > ***@***.**** commented on this gist. > ------------------------------ > > 420B is returned by this particular variant of crc16 if you feed it with > b'45377 So if you can figure out the connection between that & your list > you're good to go. Unfortunately nothing obvious comes to mind. > … <#m_6125718102667563380_m_-2639103623622540039_> > > Well converting it from binary to hexadecimal it’s 0x92 and according to > https://crccalc.com/ that should return 420B for CRC-16-CCITT-FALSE. If > that is a different one than the above code, how can i change the code for > this variant that i need? > > — > Reply to this email directly, view it on GitHub > <https://gist.github.com/oysstu/68072c44c02879a2abf94ef350d1c7c6#gistcomment-4550183> > or unsubscribe > <https://github.com/notifications/unsubscribe-auth/AV562M27VG3QMPOCZ3JCZHDXDIPURBFKMF2HI4TJMJ2XIZLTSKBKK5TBNR2WLJDHNFZXJJDOMFWWLK3UNBZGKYLEL52HS4DFQKSXMYLMOVS2I5DSOVS2I3TBNVS3W5DIOJSWCZC7OBQXE5DJMNUXAYLOORPWCY3UNF3GS5DZVRZXKYTKMVRXIX3UPFYGLK2HNFZXIQ3PNVWWK3TUUZ2G64DJMNZZDAVEOR4XAZNEM5UXG5FFOZQWY5LFVAZTOMRWGU4DSOFHORZGSZ3HMVZKMY3SMVQXIZI> > . > You are receiving this email because you commented on the thread. > > Triage notifications on the go with GitHub Mobile for iOS > <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> > or Android > <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub> > . > >

return('{:04X}'.format(crc))

Thanks, it works. Is there a better way to convert the list to be in a suitable format than this ChatGPT suggestion? (i'm very new to python)
bits_string = ''.join(str(bit) for bit in input_list)
int_value = int(bits_string, 2)
hex_value = hex(int_value)
hex_string = hex_value.replace('0x', '0x0') if len(hex_value) % 2 == 1 else hex_value
hex_value = bytes.fromhex(hex_string[2:])
crc=crc16(hex_value)

fromhex won't work if you're using upython? You could try import binascii bits_string = ''.join(str(bit) for bit in input_list) int_value = int(bits_string, 2) hex = hex(int_value)[2:] hex_value = binascii.unhexlify(hex)

…

On Thu, 27 Apr 2023 at 19:03, TrajcheKrstev ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ return('{:04X}'.format(crc)) Thanks, it works. Is there a better way to convert the list to be in a suitable format than this ChatGPT suggestion? bits_string = ''.join(str(bit) for bit in input_list) int_value = int(bits_string, 2) hex_value = hex(int_value) hex_string = hex_value.replace('0x', '0x0') if len(hex_value) % 2 == 1 else hex_value hex_value = bytes.fromhex(hex_string[2:]) crc=crc16(hex_value) — Reply to this email directly, view it on GitHub <https://gist.github.com/oysstu/68072c44c02879a2abf94ef350d1c7c6#gistcomment-4550238> or unsubscribe <https://github.com/notifications/unsubscribe-auth/AV562M34PM55UV4Y3T4S5PTXDIY53BFKMF2HI4TJMJ2XIZLTSKBKK5TBNR2WLJDHNFZXJJDOMFWWLK3UNBZGKYLEL52HS4DFQKSXMYLMOVS2I5DSOVS2I3TBNVS3W5DIOJSWCZC7OBQXE5DJMNUXAYLOORPWCY3UNF3GS5DZVRZXKYTKMVRXIX3UPFYGLK2HNFZXIQ3PNVWWK3TUUZ2G64DJMNZZDAVEOR4XAZNEM5UXG5FFOZQWY5LFVAZTOMRWGU4DSOFHORZGSZ3HMVZKMY3SMVQXIZI> . You are receiving this email because you commented on the thread. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub> .

@pragma31 if I have a payload like this : " 623e0200000000000000000000000000" where 623e is crc given by a software i want to verify it , so what should i pass to get this value to the function that you have written here crc16 , thanks
same if i want to use https://crccalc.com/

@oysstu could you please guide me how could I use this code.
My data is (hex) E3BCBEBEA65EB3B87266124B2B238B6B
Polynomial is 0x1021

@oysstu This line is incorrect::

6    crc = 0xFFFF

This is incorrect because your code implements a bit-serial LFSR CRC calculator, but the INIT value of 0xFFFF comes from Ross Williams' Rocksoft^tm model, which is based on a table-driven calculation.

The Rocksoft model is described in Williams' crc_v3.txt, which you can find here

In the Rocksoft model, the initial value (0xFFFF) is loaded into the register, and the current contents of the register are XOR'd with the next incoming data bytes at the start of each iteration. You can see this in Williams' sample C code. Line 1635 in crc_v3.txt shows the INIT value being loaded into the register (p_cm->cm_reg), and line 1649 shows the data bytes being XOR'd into p_cm->cm_reg.

By preloading a serial LFSR with 0xFFFF, you're effectively prepending 0xFFFF to your block of data, which doesn't give the same result. What you actually want to do is XOR 0xFFFF with the first two bytes of data.

I recommend testing your algorithm against the calculator at sunshine2k.de. It gives correct results.