pycrc

pycrc is a free, easy to use Cyclic Redundancy Check (CRC) calculator and source code generator.

Index^¶

Description
Documentation
List of supported CRC models
Download
News
To Do
CRC links

Description^¶

pycrc provides CRC reference implementations in Python and a source code generator for C. The used CRC variant can be chosen from a fast but space-consuming implementation to slower but smaller versions especially suitable for embedded applications. The models can be freely chosen, but a comprehensive collection of CRC models is available by name. The following functions are implemented:

• calculate the checksum of a string or a file.
• generate the source files for a "C" implementation.

The following variants of the CRC algorithm are supported:

• bit-by-bit: the basic algorithm which operates individually on every bit of the augmented message (i.e. the input data with width 0-bits attached to the end). This algorithm is the easiest one to understand, because it's a direct implementation of the basic polynomial division, but it is also the slowest among all possible variants.
• bit-by-bit-fast: a variation of the simple bit-by-bit algorithm, which doesn't need the augmented message. This algorithm might be a good choice for embedded platforms, where code space is a major concern.
• table-driven: the standard table driven algorithm. This algorithm works only with models where width is a multiple of 8. This is the fastest variant, because it operates on bytes as opposed to bits, and uses a look-up table of 256 elements, which might not be feasible for small embedded systems, though. Anyway, the number of elements in the look-up table can be reduced by means of the --table_idx_with command line switch. By using 4 bits (16 elements in the look-up table) a significant speed-up can be measured with respect to the bit-by-bit algorithms.

pycrc is released under the terms of the MIT licence.

Documentation^¶

Man page
List of supported CRC models
FAQ
pycrc-users Mailing list

Download^¶

The most recent version is:
pycrc-0.7.1.tar.gz
pycrc-0.7.1.zip

Older versions can be downloaded from sourceforge.net.

News^¶

Version 0.7.1 released  (05 April 2009)
Version 0.7.1 is only a small feature enhancement release:

• a new CRC model, crc-32mpeg was added. Thanks to Thomas Edwards.

Please check the ChangeLog file for a detailed list of changes.

Version 0.7 released  (27 February 2009)
Version 0.7 of pycrc fixes a small bug and adds two new command line options:

• added --direct option. Now it is possible to select 'direct' and 'not direct' version of the algorithm.
• added --check-hexstring option. With this option it is possible to check a hexadecimal number on-the-fly. Closes issue 2545183. Thanks to Arnim Littek.
• added a check for extra arguments on the command line. Previously, additional arguments were silently ignored. Closes issue 2545185. Thanks to Arnim Littek.

Please check the ChangeLog file for a detailed list of changes.

Version 0.6.7 released  (11 December 2008)
Version 0.6.7 of pycrc is just a small bugfix release:

• The code should run on both Python 2.x and 3.0.
• Fixed a bug that gave wrong results on x64 platforms.
• Fixed a bug that raised an exception when an unknown model was selected.

Please check the ChangeLog file for a detailed list of changes.

All news can be read in the pycrc news archive.

To Do^¶

pycrc is considered stable code. No new features are planned, but bugs are still fixed and new models added on request.

Check out pycrc's issue tracker for other open bugs and feature requests.

CRC links^¶

• Ross N. Williams' Painless Guide to CRC Error Detection Algorithms is a very good starting point to understand CRC algorithms.
• The online CRC calculator has been heavily used in the early stage of pycrc. It is a very good place to test your CRC implementation and the C implementation on this site is worth studying.
• The WikiPedia-page on Cyclic redundancy check contains a rather scientific (i.e. dry) explanation of the matter, but the links on the bottom of the page are very useful.
• The Catalogue of Parameterised CRC Algorithms by Rainstorm contains a lot of useful information about CRC variants.
• Terry Ritter's The Great CRC Mystery is another good place to study CRC algorithms.

Other Free CRC tools^¶

• crc-generator is a Python module which calculates the CRC and generates C source code. (MIT licence)
• CrcMoose is another CRC Python module, able to generate a CRC of arbitrary models and it contains a long list of CRC models. (MIT licence)
• Universal Crc is a C program that generates fast C source code. It is noteworthy that it can generate a table-driven algorithm for polynoms which do not have to be 8-bit aligned. (GPL licence)