crcmod.predefined – CRC calculation using predefined algorithms

This module provides a function factory mkPredefinedCrcFun() and a class PredefinedCrc for calculating CRCs of byte strings using common predefined CRC algorithms.

The function factory and the class are very similar to those defined in crcmod, except that the CRC algorithm is specified by a predefined name, rather than the individual polynomial, reflection, and initial and final-XOR parameters.

Predefined CRC algorithms

The crcmod.predefined module offers the following predefined algorithms:

Name	Polynomial	Reversed?	Init-value	XOR-out	Check
crc-8	0x107	False	0x00	0x00	0xF4
crc-8-darc	0x139	True	0x00	0x00	0x15
crc-8-i-code	0x11D	False	0xFD	0x00	0x7E
crc-8-itu	0x107	False	0x55	0x55	0xA1
crc-8-maxim	0x131	True	0x00	0x00	0xA1
crc-8-rohc	0x107	True	0xFF	0x00	0xD0
crc-8-wcdma	0x19B	True	0x00	0x00	0x25
crc-16	0x18005	True	0x0000	0x0000	0xBB3D
crc-16-buypass	0x18005	False	0x0000	0x0000	0xFEE8
crc-16-dds-110	0x18005	False	0x800D	0x0000	0x9ECF
crc-16-dect	0x10589	False	0x0001	0x0001	0x007E
crc-16-dnp	0x13D65	True	0xFFFF	0xFFFF	0xEA82
crc-16-en-13757	0x13D65	False	0xFFFF	0xFFFF	0xC2B7
crc-16-genibus	0x11021	False	0x0000	0xFFFF	0xD64E
crc-16-maxim	0x18005	True	0xFFFF	0xFFFF	0x44C2
crc-16-mcrf4xx	0x11021	True	0xFFFF	0x0000	0x6F91
crc-16-riello	0x11021	True	0x554D	0x0000	0x63D0
crc-16-t10-dif	0x18BB7	False	0x0000	0x0000	0xD0DB
crc-16-teledisk	0x1A097	False	0x0000	0x0000	0x0FB3
crc-16-usb	0x18005	True	0x0000	0xFFFF	0xB4C8
x-25	0x11021	True	0x0000	0xFFFF	0x906E
xmodem	0x11021	False	0x0000	0x0000	0x31C3
modbus	0x18005	True	0xFFFF	0x0000	0x4B37
kermit [1]	0x11021	True	0x0000	0x0000	0x2189
crc-ccitt-false [1]	0x11021	False	0xFFFF	0x0000	0x29B1
crc-aug-ccitt [1]	0x11021	False	0x1D0F	0x0000	0xE5CC
crc-24	0x1864CFB	False	0xB704CE	0x000000	0x21CF02
crc-24-flexray-a	0x15D6DCB	False	0xFEDCBA	0x000000	0x7979BD
crc-24-flexray-b	0x15D6DCB	False	0xABCDEF	0x000000	0x1F23B8
crc-32	0x104C11DB7	True	0x00000000	0xFFFFFFFF	0xCBF43926
crc-32-bzip2	0x104C11DB7	False	0x00000000	0xFFFFFFFF	0xFC891918
crc-32c	0x11EDC6F41	True	0x00000000	0xFFFFFFFF	0xE3069283
crc-32d	0x1A833982B	True	0x00000000	0xFFFFFFFF	0x87315576
crc-32-mpeg	0x104C11DB7	False	0xFFFFFFFF	0x00000000	0x0376E6E7
posix	0x104C11DB7	False	0xFFFFFFFF	0xFFFFFFFF	0x765E7680
crc-32q	0x1814141AB	False	0x00000000	0x00000000	0x3010BF7F
jamcrc	0x104C11DB7	True	0xFFFFFFFF	0x00000000	0x340BC6D9
xfer	0x1000000AF	False	0x00000000	0x00000000	0xBD0BE338
crc-64	0x1000000000000001B	True	0x0000000000000000	0x0000000000000000	0x46A5A9388A5BEFFE
crc-64-we	0x142F0E1EBA9EA3693	False	0x0000000000000000	0xFFFFFFFFFFFFFFFF	0x62EC59E3F1A4F00A
crc-64-jones	0x1AD93D23594C935A9	True	0xFFFFFFFFFFFFFFFF	0x0000000000000000	0xCAA717168609F281

Notes

[1] (1,2,3)

Definitions of CCITT are disputable. See:

• http://homepages.tesco.net/~rainstorm/crc-catalogue.htm

• http://web.archive.org/web/20071229021252/http://www.joegeluso.com/software/articles/ccitt.htm

mkPredefinedCrcFun() – CRC function factory

The function factory provides a simple interface for CRC calculation. It is similar to crcmod.mkCrcFun(), except that it specifies a CRC algorithm by name rather than its parameters.

crcmod.predefined.mkPredefinedCrcFun(crc_name)

Function factory that returns a new function for calculating CRCs using a specified CRC algorithm.

Parameters:

crc_name (string) – The name of the predefined CRC algorithm to use.

Returns:

CRC calculation function

Return type:

function

The function that is returned is the same as that returned by crcmod.mkCrcFun():

.crc_function(data[, crc=initCrc])

Parameters:

• data (byte string) – Data for which to calculate the CRC.

• crc – Initial CRC value.

Returns:

Calculated CRC value.

Return type:

integer

crcmod.predefined.mkCrcFun(crc_name)

This is an alias for crcmod.predefined.mkPredefinedCrcFun(). However, it is not defined when crcmod.predefined is imported using the form:

>>> from crcmod.predefined import *

Examples

CRC-32 example:

>>> import crcmod.predefined

>>> crc32_func = crcmod.predefined.mkCrcFun('crc-32')
>>> hex(crc32_func('123456789'))
'0xcbf43926L'

XMODEM example:

>>> xmodem_crc_func = crcmod.predefined.mkCrcFun('xmodem')
>>> hex(xmodem_crc_func('123456789'))
'0x31c3'

Class PredefinedCrc

This class is inherited from the crcmod.Crc class, and is the same except for the initialization. It specifies a CRC algorithm by name rather than its parameters.

class crcmod.predefined.PredefinedCrc(crc_name)

Returns a new Crc object for calculating CRCs using a specified CRC algorithm.

The parameter is the same as that for the factory function crcmod.predefined.mkPredefinedCrcFun().

Parameters:

crc_name (string) – The name of the predefined CRC algorithm to use.

class crcmod.predefined.Crc(poly[, initCrc, rev, xorOut])

This is an alias for crcmod.predefined.PredefinedCrc. However, it is not defined when crcmod.predefined is imported using the form:

>>> from crcmod.predefined import *

Examples

CRC-32 Example:

>>> import crcmod.predefined

>>> crc32 = crcmod.predefined.Crc('crc-32')
>>> crc32.update('123456789')
>>> hex(crc32.crcValue)
'0xcbf43926L'
>>> crc32.hexdigest()
'CBF43926'