crystal-crc

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CRC (Cyclic Redundancy Check) algorithms for Crystal. Based on the digest-crc Ruby library and should be API compatible.

Features

• Provides support for the following CRC algorithms:
  • CRC1
  • CRC5
  • CRC8
  • CRC8_1Wire
  • CRC15
  • CRC16
  • CRC16CCITT
  • CRC16DNP
  • CRC16Genibus
  • CRC16Kermit
  • CRC16Modbus
  • CRC16USB
  • CRC16X25
  • CRC16XModem
  • CRC16ZModem
  • CRC16QT
  • CRC24
  • CRC32
  • CRC32c
  • CRC32BZip2
  • CRC32Jam
  • CRC32MPEG
  • CRC32POSIX
  • CRC32XFER
  • CRC64
  • CRC64Jones
  • CRC64XZ
• Pure Crystal implementation.
• Uses Crystal's Digest class.
• Provides CRC Tables for optimized calculations.

Installation

1. Add the dependency to your shard.yml:

   dependencies:
     crc:
       github: postmodern/crystal-crc
       version: ~> 1.0
   

2. Run shards install

Examples

Calculate a CRC32:

require "crc/crc32"

CRC::CRC32.hexdigest("hello")
# => "3610a686"

Calculate a CRC32 of a file:

CRC::CRC32.file("README.md")
# => #<CRC::CRC32: 127ad531>

Incrementally calculate a CRC32:

crc = CRC::CRC32.new
crc << "one"
crc << "two"
crc << "three"
crc.hexdigest
# => "09e1c092"

Directly access the checksum:

crc.checksum
# => 165789842

Defining your own CRC class:

require "crc/crc32"

module CRC
  class CRC3000 < CRC32

    class_getter init_crc = 0xffffffff_u32

    class_getter xor_mask = 0xffffffff_u32

    TABLE = [
      # ....
    ].freeze

    @table = TABLE

    def update_impl(data : Bytes) : Nil
      data.each do |b|
        @crc = (((@crc >> 8) & 0x00ffffff) ^ @table[(@crc ^ b) & 0xff])
      end
    end
  end
end

Benchmarks

$ crystal build --release benchmarks.cr
$ ./benchmarks
Generating 1000 8.0Kb lengthed strings ...
Benchmarking CRC classes ...
                                  user     system      total        real
CRC1#update           0.007390   0.000051   0.007441 (  0.007474)
CRC5#update           0.033173   0.000000   0.033173 (  0.033430)
CRC8#update           0.033643   0.000000   0.033643 (  0.033919)
CRC81Wire#update      0.032657   0.000000   0.032657 (  0.032891)
CRC15#update          0.050786   0.000000   0.050786 (  0.051130)
CRC16#update          0.037301   0.000000   0.037301 (  0.037543)
CRC16CCITT#update     0.047864   0.000000   0.047864 (  0.048261)
CRC16DNP#update       0.039589   0.000000   0.039589 (  0.039888)
CRC16Genibus#update   0.046829   0.000000   0.046829 (  0.047099)
CRC16Modbus#update    0.038705   0.000000   0.038705 (  0.038995)
CRC16QT#update        0.054050   0.000000   0.054050 (  0.054395)
CRC16USB#update       0.039959   0.000000   0.039959 (  0.040305)
CRC16X25#update       0.039422   0.000000   0.039422 (  0.039882)
CRC16XModem#update    0.048175   0.000000   0.048175 (  0.048596)
CRC16ZModem#update    0.046812   0.000000   0.046812 (  0.047062)
CRC24#update          0.053732   0.000000   0.053732 (  0.054109)
CRC32#update          0.037498   0.000000   0.037498 (  0.037701)
CRC32BZip2#update     0.043699   0.000000   0.043699 (  0.044046)
CRC32c#update         0.038263   0.000000   0.038263 (  0.038508)
CRC32Jam#update       0.039061   0.000000   0.039061 (  0.039361)
CRC32Mpeg#update      0.044015   0.000000   0.044015 (  0.044523)
CRC32POSIX#update     0.043790   0.000000   0.043790 (  0.044116)
CRC32XFER#update      0.043419   0.000000   0.043419 (  0.043683)
CRC64#update          0.034250   0.000000   0.034250 (  0.034411)
CRC64Jones#update     0.034213   0.000000   0.034213 (  0.034438)
CRC64XZ#update        0.034999   0.000000   0.034999 (  0.035243)

Development

CRC TABLE values for common CRC algorithms can be obtained from the pycrc tool:

./pycrc.py --algorithm=table-driven --model=crc-32 --generate=c

Contributing

1. Fork it (https://github.com/postmodern/crystal-crc/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• Postmodern - creator and maintainer