PYCRC
pycrc is a free, fully parametrisable Cyclic Redundancy Check (CRC) calculator and C source code generator written in Python.
Index
DescriptionDocumentation
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 cosen, 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 pageList of supported CRC models
FAQ
pycrc-users Mailing list
Download
The most recent version is:pycrc-0.6.6.tar.gz
pycrc-0.6.6.zip
Older versions can be downloaded from sourceforge.net.
News
Version 0.6.6 released
(06 June 2008)
Version 0.6.6 of pycrc is just a small bugfix release:
- Fixed a bug in the print_params function. Closes issue 1985197. Thanks to Artur Lipowski.
- Creative Commons license for the documentation.
Version 0.6.5 released
(02 March 2008)
Version 0.6.5 of adds a few new CRC models (dallas-1-wire, r-crc-16, thanks to "raimondo") and contains the following changes:
- fixed a problem with the generated code for bit-by-bit-fast algorithms. Thanks to Hans Bacher.
- added extern "C" declaration to the generated C header file. Thanks to Nathan Royer.
- added --crc-type and --include-file options.
Version 0.6.4 released
(05 December 2007)
Version 0.6.4 fixes the following bugs:
- Fixed issue 1843774: The code does not work for multiple calls to crc_update().
All news can be read in the pycrc news archive.
To Do
- add more algorithms, optimise existing ones
- Create a performance and code-space table for the different algorithms
- add error correcting codes as well(?)
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 does not have to be 8-bit aligned. (GPL licence)