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@oysstu
Last active Sep 23, 2022
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Implementation of crc16 (CRC-16-CCITT) in python
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
@eadmaster
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eadmaster commented Jan 22, 2018

is it ok if i remove the numpy dependency with ctypes?

return (ctypes.c_ushort(crc)).value

@Theroin
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Theroin commented Feb 15, 2018

 ''''-*- coding: utf-8 -*-
return 19255 0x4B37 '''
import numpy as np

def crc16(data: bytes):
    '''
    CRC-16-ModBus Algorithm
    '''
    data = bytearray(data)
    poly = 0xA001
    crc = 0xFFFF
    for b in data:
        crc ^= (0xFF & b)
        for _ in range(0, 8):
            if (crc & 0x0001):
                crc = ((crc >> 1) & 0xFFFF) ^ poly
            else:
                crc = ((crc >> 1) & 0xFFFF)

    return np.uint16(crc)
    
    
print(crc16(b'\x31\x32\x33\x34\x35\x36\x37\x38\x39'))

@oysstu
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oysstu commented Aug 19, 2018

Replaced numpy dependency with a simple crc & 0xFFFF

@dbedrenko
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dbedrenko commented May 21, 2019

This does not seem to give the correct answer when compared to http://crccalc.com and the CRC16 implementation of a firmware I'm dealing with.

> hex(crc16(b'\x31\x32\x33\x34\x35\x36\x37\x38\x39'))
0x6e90
> hex(crc16(b'\x31\x32\x33\x34\x35\x36\x37\x38\x39', 0x1021))
0x45e2

Neither of which give the expected 0xE5CC, see link: https://crccalc.com/?crc=313233343536373839&method=crc16&datatype=hex

@nightuser
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nightuser commented Oct 20, 2019

@dbedrenko: This code is equivalent to CRC-16/X-25 in your link (the byte order is different, but it's easy to change). Also, this code uses inverted values (like ~0x1021) for everything.

@prathamOvalekarDajac
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prathamOvalekarDajac commented Oct 29, 2020

https://gist.github.com/nightuser I am trying the CRC-16/X25, But I am unable get the correct answer.

@nightuser
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nightuser commented Oct 29, 2020

@prathamOvalekarDajac: Did you use ~0x1021 as the value of poly?

@prathamOvalekarDajac
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prathamOvalekarDajac commented Oct 29, 2020

`def crc16(data: bytes):
'''
CRC-16-CCITT Algorithm
'''
poly= ~0x1021
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

print(crc16(b'\x00\x50\x03'))`

@daffodilistic
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daffodilistic commented Jul 12, 2021

Note that https://crccalc.com/ does not convert ASCII inputs with spaces properly. Hope this helps.

@pragma31
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pragma31 commented Oct 28, 2021

def crc16(data: bytes):
    '''
    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
    return crc

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