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Viewing File: crcmod.predefined.rst
:mod:`crcmod.predefined` -- CRC calculation using predefined algorithms
=======================================================================
.. module:: crcmod.predefined
:synopsis: CRC calculation using predefined algorithms
.. moduleauthor:: Craig McQueen
.. sectionauthor:: Craig McQueen
This module provides a function factory :func:`mkPredefinedCrcFun` and a class :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 :mod:`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 :mod:`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`` [#ccitt]_ 0x11021 True 0x0000 0x0000 0x2189
``crc-ccitt-false`` [#ccitt]_ 0x11021 False 0xFFFF 0x0000 0x29B1
``crc-aug-ccitt`` [#ccitt]_ 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
================================ ====================== ========== ==================== ==================== ====================
.. rubric:: Notes
.. [#ccitt] 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
:func:`mkPredefinedCrcFun` -- CRC function factory
--------------------------------------------------
The function factory provides a simple interface for CRC calculation. It is similar
to :func:`crcmod.mkCrcFun`, except that it specifies a CRC algorithm by name rather
than its parameters.
.. function:: mkPredefinedCrcFun(crc_name)
Function factory that returns a new function for calculating CRCs
using a specified CRC algorithm.
:param crc_name: The name of the predefined CRC algorithm to use.
:type crc_name: string
:return: CRC calculation function
:rtype: function
The function that is returned is the same as that returned by :func:`crcmod.mkCrcFun`:
.. function:: .crc_function(data[, crc=initCrc])
:param data: Data for which to calculate the CRC.
:type data: byte string
:param crc: Initial CRC value.
:return: Calculated CRC value.
:rtype: integer
.. function:: mkCrcFun(crc_name)
This is an alias for :func:`crcmod.predefined.mkPredefinedCrcFun`. However, it is not defined when
:mod:`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 :class:`PredefinedCrc`
----------------------------
This class is inherited from the :class:`crcmod.Crc` class, and is the same except for the
initialization. It specifies a CRC algorithm by name rather than its parameters.
.. class:: PredefinedCrc(crc_name)
Returns a new :class:`Crc` object for calculating CRCs using a specified CRC algorithm.
The parameter is the same as that for the factory function :func:`crcmod.predefined.mkPredefinedCrcFun`.
:param crc_name: The name of the predefined CRC algorithm to use.
:type crc_name: string
.. class:: Crc(poly[, initCrc, rev, xorOut])
This is an alias for :class:`crcmod.predefined.PredefinedCrc`. However, it is not defined when
:mod:`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'
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