CRC32C Checksum Library

2.8 · active · verified Mon Apr 06

The `crc32c` Python package provides an implementation of the CRC32C checksum algorithm, intelligently leveraging hardware acceleration (Intel SSE 4.2, ARMv8 crc32 instructions) when available, and falling back to an optimized software implementation otherwise. As of version 2.8, it offers robust data integrity verification across various platforms. The library aims for regular updates.

Warnings

deprecated The `crc32c.crc32` function is deprecated and will be removed in future versions. Users should switch to `crc32c.crc32c` for all checksum calculations.
Fix: Replace `crc32c.crc32(...)` with `crc32c.crc32c(...)`.
gotcha The `auto` value for the `CRC32C_SW_MODE` environment variable, which controls software fallback behavior, is planned for discontinuation. It's recommended to explicitly use `force` or `none` if specific fallback control is needed.
Fix: If setting `CRC32C_SW_MODE`, use `force` to always use software implementation or `none` to raise an error if hardware is unavailable, instead of `auto`.
breaking In versions up to 2.6, an `ImportError` was raised if no hardware support was found and software fallback was not enabled. As of version 2.7, this behavior has changed: `CRC32C_SW_MODE='none'` will now issue a `RuntimeWarning` on import and a `RuntimeError` on execution if hardware support is missing.
Fix: Update exception handling for `crc32c` import/execution to catch `RuntimeWarning` or `RuntimeError` when `CRC32C_SW_MODE='none'` is set, instead of `ImportError`.
gotcha The project uses specific `gcc`/`clang` compiler extensions. If installing from source (e.g., when no pre-built wheel is available for your platform/Python version), older compiler versions might fail to build the package.
Fix: Ensure your C/C++ compiler (gcc/clang/Visual Studio) is up-to-date and supports modern extensions. Using a platform with pre-built binary wheels from PyPI is the easiest way to avoid this.

Install

pip install crc32c Install crc32c

Imports

crc32c
```
import crc32c
```
Main module import
crc32c
```
crc32c.crc32c(data)
```
The 'crc32c.crc32' function is deprecated; use 'crc32c.crc32c' instead for the core checksum calculation.
CRC32CHash
```
from crc32c import CRC32CHash
```
For streaming checksum calculations with a hash-like object.

Quickstart

Demonstrates basic CRC32C calculation, incremental updates, usage of the `CRC32CHash` object, and how to check for hardware acceleration.

import crc32c

# Calculate CRC32C for a byte string
data = b"hello world"
checksum = crc32c.crc32c(data)
print(f"CRC32C checksum of '{data.decode()}': {checksum}")

# Incremental calculation (similar to binascii.crc32 with 'value' parameter)
crc_part1 = crc32c.crc32c(b"hello")
crc_total = crc32c.crc32c(b" world", value=crc_part1)
print(f"Incremental CRC32C: {crc_total}")

# Using the hash-like object
hash_obj = crc32c.CRC32CHash()
hash_obj.update(b"hello")
hash_obj.update(b" world")
print(f"CRC32CHash object checksum: {hash_obj.checksum}")

# Check if hardware acceleration is in use
print(f"Hardware acceleration in use: {crc32c.hardware_based}")

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