crc8-pure

Zero-dependency, pure-Python CRC-8 over 7 RevEng-catalogued variants.

crc8-pure provides a single, self-contained implementation of seven widely used CRC-8 variants — crc-8, crc-8-darc, crc-8-i-code, crc-8-itu (CCITT), crc-8-maxim (DOW), crc-8-rohc, and crc-8-wcdma — together with a class-based incremental API and a command-line entry point. No C-extension dependencies; only the Python standard library is used at runtime.

Install

pip install crc8-pure

Or from a local checkout:

pip install -e .

Requires Python ≥ 3.8. There are no runtime dependencies.

Quickstart

import crc8_pure

# Functional API: returns an int 0–255
crc8_pure.crc8(b"hello")                  # crc-8 variant (default)
crc8_pure.crc8(b"hello", variant="crc-8-maxim")
crc8_pure.crc8_maxim(b"hello")            # convenience wrapper

# Incremental / streaming API
crc8_pure.crc8(b"hel", init=0x00)
crc8_pure.crc8(b"lo", init=<prev>)        # continues from previous state

# Class API
h = crc8_pure.CRC8(variant="crc-8-maxim")
h.update(b"hello")
h.digest()                                # -> bytes
h.hexdigest()                             # -> "3b"

CLI

# String input
python -m crc8_pure crc8-maxim "123456789"

# Hex-prefixed output
python -m crc8_pure crc8 "123456789" --hex

# File input
python -m crc8_pure crc8-maxim path/to/file.bin

# Read from stdin
cat file.bin | python -m crc8_pure crc-8 -

7 Variants

Check values come from the RevEng CRC Catalogue and have been verified byte-exact against crcmod.

Aliases: CCITT → crc-8-itu, MAXIM → crc-8-maxim, DOW-CRC → crc-8-maxim.

API

crc8(data=b"", variant="crc-8", init=None) -> int

Compute a CRC-8 checksum. init lets you resume from a previous partial result: crc8(b"lo", init=crc8(b"hel")) is equivalent to crc8(b"hello").

CRC8(variant="crc-8", init=None)

Incremental calculator. Use update(data) to feed bytes, then digest() (bytes) or hexdigest() (string).

CLI

python -m crc8_pure <variant> [FILE_OR_STRING...] [--hex]

If no input is given (or -), data is read from stdin. A single argument is treated as a file path if it exists, otherwise as a string literal. Multiple arguments are concatenated.

Tests

pip install pytest
pytest -q

The test suite covers all 21 canonical vectors (3 inputs × 7 variants) plus boundary conditions, alias resolution, incremental equivalence, class API, and CLI smoke tests.

Current test count: 126 tests.

Known Issues / Limitations

The following are honest documented limits of crc8-pure:

• CRC-8 is not cryptographic. CRC-8 is for error-detection on trusted media; do not use it as a cryptographic integrity check or MAC.
• CLI stdin/file materialization. python -m crc8_pure <variant> <file> fully materializes the file into RAM before processing. For multi-GB inputs this may exhaust memory; no streaming boundary is applied.
• Thread-safety. A CRC8 instance is not safe for concurrent update() calls from multiple threads; create one instance per thread.
• data accepts non-bytes silently. Pass bytes-like objects (bytes/bytearray/ memoryview). Passing a non-bytes value will produce a non-canonical result without raising an error.
• No CRC8.copy() / CRC8.reset(). Re-using a CRC8 instance requires constructing a new one; there is no copy() or reset() method.

License

MIT — see LICENSE.