crc32c 2.1

A python package implementing the crc32c algorithmin hardware and software

This package implements the crc32c checksum algorithm. It automatically chooses between a hardware-based implementation (using the CRC32C SSE 4.2 instruction of Intel CPUs, and the crc32* instructions on ARMv8 CPUs), or a software-based one when no hardware support can be found.

Because crc32c is in PyPI, you can install it with:

pip install crc32c

Supported platforms are Linux and OSX using the gcc and clang compilers, and Windows using the Visual Studio compiler. Other compilers in Windows (MinGW for instance) might work. Binary wheels are also provided in PyPI for major platforms/architectures.

Usage

The only method exposed by this module is crc32c(data, [crc]). It computes the CRC32C checksum of data starting with an initial crc checksum, similarly to how the built-in binascii.crc32 works. It can thus be used like this:

print(crc32c.crc32c(b'hello world'))
# 3381945770
crc = crc32c.crc32c(b'hello')
print(crc32c.crc32c(b' world', crc))
# 3381945770

In older versions, the function exposed by this module was called crc32. That name is still present but deprecated, and will be removed in new versions of the library.

Additionally one can consult the hardware_based module-level value to check if the algorithm currently in use is software- or hardware-based.

Implementation details

By default, if your CPU doesn’t have CRC32C hardware support, the package will fallback to use a software implementation of the crc32c checksum algorithm. This behavior can be changed by setting the CRC32C_SW_MODE environment variable to one of the following values:

• auto: same as if unset, will eventually be discontinued.

• force: use software implementation regardless of hardware support.

• none: fail to import the module with an ImportError if no hardware support is found (old 1.x default behavior).

Both the hardware- (Intel) and software-based algorithms are based on Mark Adler’s code, with some modifications required to make the code more portable and fit for inclusion within this python package. The ARMv8 hardware implementation is based on Google’s crc32c C++ library.

Copyright

This package is copyrighted:

ICRAR - International Centre for Radio Astronomy Research
(c) UWA - The University of Western Australia, 2017
Copyright by UWA (in the framework of the ICRAR)

The original crc32c algorithms, both software and Intel-hardware, are copyrighted by:

Copyright (C) 2013 Mark Adler

The crc32c ARMv8 hardware code is copyrighted by:

Copyright 2017 The CRC32C Authors

License

This package is licensed under the LGPL-2.1 license.

The original crc32c code, both software and for Intel SSE4.2 machines, are licensed under the BSD 3-clause license.

The original crc32c code for ARM64 machines is licensed under a BSD-style license that can be found in the LICENSE file of Google’s crc32c.