# CRC

This is a Julia module for calculating Cyclic Redundancy Checksums (CRCs).

• 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("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.

The returned function can also be called with a file handle, so calling open(crc32, file) will return the checksum of file.

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)("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)
CRC.Spec{UInt8}(7, 0x09, 0x00, false, false, 0x00, 0x75)

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


Of course, this is already defined:

julia> CRC_7
CRC.Spec{UInt8}(7, 0x09, 0x00, false, false, 0x00, 0x75)


## Installation

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

julia> Pkg.add("CRC")


## Versions

• 4.0.0 - 2020-11-27 Remove command line functionality.

• 3.1.0 - 2020-11-07 Update ArgParse dependency and add Project.toml.

• 3.0.0 - 2018-02-28 Update for Julia 1.0

• 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).