CRC

This module is used to calculate CRC (Cyclic Redundancy Check) values for binary data. It uses NIF functions written in C to iterate over the given binary calculating the CRC checksum value. The NIFs are written to report their time slice usage and will not interfere with the schedulers.

Installation

1. Add crc to your list of dependencies in mix.exs:

  def deps do
    [{:crc, "~> 0.8"}]
  end

Supported algorithms (models)

Run CRC.list/0 to get a full list of all pre-defined models or CRC.list/1 with a filter to search for a pre-defined model.

Usage

To calculate a CRC-16 X-Modem checksum for the binary <<1,2,3,4,5,4,3,2,1>> using the pre-defined model:

iex> CRC.crc(:crc_16_xmodem, <<1,2,3,4,5,4,3,2,1>>)
31763

You can also create model's at runtime and re-use them. This can be done with a map:

iex> model = CRC.crc_init(
  %{
    width: 16,
    poly: 0x1021,
    init: 0x00,
    refin: false,
    refout: false,
    xorout: 0x00
  }
)
#Reference<x.x.x.x>
iex> CRC.crc(model, <<1,2,3,4,5,4,3,2,1>>)
31763

Or extend pre-defined models:

iex> model = CRC.crc_init(
  %{
    extend: :crc_16_xmodem,
    init: 0x00,
  }
)
#Reference<x.x.x.x>
iex> CRC.crc(model, <<1,2,3,4,5,4,3,2,1>>)
31763

Tests

CRC implementations have been tested against these online calculators to validate their correctness to the best of our ability.

• https://www.lammertbies.nl/comm/info/crc-calculation.html
• http://www.sunshine2k.de/coding/javascript/crc/crc_js.html

There are also two property tests that can use PyCRC or CRC RevEng if installed and configured locally.

$ export PYCRC_BIN=~/pycrc-0.9.1/pycrc.py
$ export REVENG_BIN=~/reveng-1.5.2/reveng
$ mix test

PyCRC is used as a part of the TravisCI test suite.