Module: LZW

Extended by:
LZW
Included in:
LZW
Defined in:
lib/lzw.rb,
lib/lzw/version.rb

Overview

Scaling LZW, like Unix compress(1)

The LZW gem offers:

LZW

Simple functional interface

Compressor

LZW compressor with more fine-grained controls

Decompressor

LZW decompressor in the same vein

BitBuf

A String-backed buffer allowing bit-level operations

compress-lzw

API Documentation

About

This gem is a Ruby implementation of the Lempel-Ziv-Welch compression algorithm created in 1984. As of 2004, all patents on it had expired.

This implementation is compatible with the classic unix compress tool, and not compatible with the LZW compression used within GIF streams.

LZW is notable in two ways: it is dictionary-based compression but does not need to pass that dictionary within its files, instead decompression relies on progressively building a dictionary in the same way as the compressor. It also works outside the boundaries of bytes, writing its dictionary codes 9 bits at a time and scaling up as the codes increase to 16 bits.

To get right to work, check out the LZW module.

TODO

  • Convert from circleci to github actions

  • Code isn't the most efficient, but get impl right first. Buffering with a queue of 8 codes makes the packed code always fit an octet boundary.

  • Add a set of tests that tries to find compress binaries installed to use for compatibility tests.

See Also:

Defined Under Namespace

Modules: Constants Classes: BitBuf, Compressor, Decompressor

Constant Summary collapse

InputStreamError =

Exception class raised when compressed input is corrupt

Class.new(RuntimeError)
VERSION = 
"0.0.2"

Instance Method Summary collapse

Instance Method Details

#compress(data) ⇒ String

Compress input with defaults

Parameters:

  • data (#each_byte) —

    data to be compressed

Returns:

  • (String) —

    LZW compressed data



27
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# File 'lib/lzw.rb', line 27

def compress(data)
  LZW::Compressor.new.compress(data)
end

#decompress(data) ⇒ String

Decompress input with defaults

Parameters:

  • data (String) —

    compressed data to be decompressed

Returns:

  • (String) —

    decompressed data

Raises:



36
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# File 'lib/lzw.rb', line 36

def decompress(data)
  LZW::Decompressor.new.decompress(data)
end