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.

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

  def deps do
    [{:crc, "~> 0.10"}]
  end

1. add crc to your rebar.config

{deps, [
  {crc, "0.10.0"}
]}.

or erlang.mk

dep_crc = hex 0.10.0

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.

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

Or you can create a model at runtime, this can be done with a map:

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

Or you can extend one of the pre-defined models:

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

CRC.crc_init/1 is used to create a resource and be used to do partial updates to a calculation that is then finalized later:

iex> resource = CRC.crc_init(:crc_16_xmodem)
#Reference<x.x.x.x>
iex> resource2 = CRC.crc_update(resource, <<1, 2, 3, 4, 5>>)
#Reference<y.y.y.y>
iex> resource3 = CRC.crc_update(resource2, <<4, 3, 2, 1>>)
#Reference<z.z.z.z>
iex>CRC.crc_final(resource3)
31763

This could be usefule to calculate a CRC for a larger binary that you are receiving asyncronously.

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.