CRC

This is a Julia module for calculating Cyclic Redundancy Checksums (CRCs). It also contains a command line tool for calculating the CRC of files.

All the algorithms in the RevEng Catalogue are supported.
New algorithms can be easily added.
Calculation can be direct or via cached tables.
Speed is comparable to optimized C (checked against CRC32 in libz).
Only arrays of bytes are accepted as data (it's certainly possible to handle arbitrary sized sequences; previous versions did this, but it complicated the code for little practical gain so I removed it - please contact me if you want me to add it back).

Examples

Calculate a CRC-32 Sum

julia> using CRC

julia> crc32 = crc(CRC_32)
(anonymous function)

julia> crc32(b"123456789")
0xcbf43926

The function crc() constructs a lookup table, which is cached in the returned function (here, crc32()). Re-using crc32() to calculate a series of CRCs is therefore more efficient than starting with crc() each time.

Within Your Program

The same example as above, but inside your program, would look like this:

using CRC
...
crc32 = crc(CRC_32)  # create our own crc function, just once
...
function some_func(...)
    ...
    x = crc32(data)  # use the crc function created above, many times
    ...
end
...

Force Direct (Tableless) Calculation

julia> crc(CRC_32, tables=NoTables)(b"123456789")
0xcbf43926

Define an Algorithm

For example, CRC-7, catalogued as width=7 poly=0x09 init=0x00 refin=false refout=false xorout=0x00 check=0x75 name="CRC-7"

julia> myCRC7 = spec(7, 0x09, 0x00, false, false, 0x00, 0x75)
Spec{Uint8}(7,0x09,0x00,false,false,0x00,0x75)

julia> @assert crc(myCRC7)(CHECK) == myCRC7.check

Of course, this is already defined:

julia> CRC_7
Spec{Uint8}(7,0x09,0x00,false,false,0x00,0x75)

From the Command Line

The main(ARGS) function is a simple utility for calculating the checksum of files:

andrew@laptop:~/project/CRC> julia -e "using CRC; main(ARGS)" -h
usage: <PROGRAM> [-l] [-d] [-c CRC] [-a] [-h] [files...]

Calculate the CRC for the given files

positional arguments:
  files          the files to read (- for stdin)

optional arguments:
  -l, --list     list available CRC algorithms
  -d, --decimal  show checksums as decimal values (default is hex)
  -c, --crc CRC  name the CRC to use (default: CRC_32)
  -a, --append   combine the data from all files
  -h, --help     show this help message and exit

andrew@laptop:~/project/CRC> alias crc='julia -e "using CRC; main(ARGS)"'
andrew@laptop:~/project/CRC> crc -l | grep "CRC_32 "
CRC_32 width=32 poly=0x04c11db7 init=0xffffffff refin=true refout=true xorout=0xffffffff check=0xcbf43926
andrew@laptop:~/project/CRC> echo -n "123456789" > /tmp/crc.txt
andrew@laptop:~/project/CRC> crc /tmp/crc.txt
0xcbf43926 /tmp/crc.txt

Note that the result matches the check value for the algorithm.

Installation

Julia can be downloaded here. Once Julia is working you can install this package using:

julia> Pkg.add("CRC")

Then, to define the crc command line utility:

alias crc='julia -e "using CRC; main(ARGS)"'

(in, for example, .alias).

Other CRC Packages

CRC32.jl is a simple implementation of CRC_32 - it is easier to understand than this code, but slower, and only supports a single CRC algorithm.
libz includes (amongst many other things) a wrapper to a C version of CRC_32 - it is similar in speed to this package (and wil be faster for short, single uses, because the lookup table is pre-calculated), but only supports that single algorithm.

Versions

1.2.0 - 2016-09-28 Drop Julia 0.3 support and switch to Libz.
1.1.0 - 2015-06-09 Small fixes for Julia 0.4, Travis + Coverage.
1.0.0 - 2014-06-31 Changed handler method so that a String is converted to bytes (instead of being treated as a file path). This will break existing code that uses the current handler (sorry!), but I hope I don't have many users (particularly users that are calling that method)!
0.2.0 - Initial release(s).

yuyichao / CRC.jl

CRC