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LZD

This is an implementation of the LZ Double-factor factorization (LZD factorization). LZD is a simple extension of the well-known compression algorithm LZ78. While LZ78 factorize an input string to the sequence of pairs of a longest previous factor and the succeeding character, LZD factorize an input string to the sequence of pairs of a longest previous factor and the succeeding longest previous factor. LZD shows better compression ratio than LZ78 in practical.

Compile

We use SCons to build source codes. To compile, you just type following command in the top of the project directory. Binary files are put in out directory.

$ scons

Note that you may have to modify some settings such as compiler in SConstruct for your environment.

Compress

Usage

$ out/lzd
Usage  : out/lzd [options]
Options: 
  -f FileName         : input file
  -o FileName         : output file
  -c                  : check whether decompressed string equals the input
  -d NUM              : set the debug level
  -l maxSize          : set max code size
  -a lz78       : LZ78
  -a lzd        : LZD
  -a vfpre      : LZD VF (Prefix Base)
  -a vfcount    : LZD VF (Count Base)
  -a vfclean    : LZD VF (Reset Base)
  -a vfpre_no_stream   : LZD VF (Prefix Base)
  -a vfcount_no_stream : LZD VF (Count Base)

Note that vfpre_no_stream, vfcount_no_stream store the input file in main memory while the compression, but vfpre, vfcount and vfclean do not.

Examples

The following command compresses SConstruct, and output to hoge.lzd by the algorithm LZD.

$ out/lzd -f SConstruct -o hoge.lzd -a lzd

The following command compresses SConstruct, and output to hoge.vfpre10 by the algorithm LZDVF Prefix Base with code size = 10.

$ out/lzd -f SConstruct -o hoge.vfpre10 -a vfpre -l 10

Decompress

Usage

% out/lzdDecompress
Usage  : out/lzdDecompress [options]
Options               : 
  -f FileName         : input file
  -o FileName         : output file
  -d NUM              : debug mode
  -a lz78       : LZ78
  -a lzd        : LZD
  -a vfpre      : LZD VF (Prefix Base)
  -a vfcount    : LZD VF (Count Base)
  -a vfclean    : LZD VF (Reset Base)
  -a vfpre_no_stream   : LZD VF (Prefix Base)
  -a vfcount_no_stream : LZD VF (Count Base)

Examples

The following command decompresses hoge.lzd compressed by LZD, and output to fuga.lzd.

$ out/lzdDecompress -f hoge.lzd -o fuga.lzd -a lzd

The following decompresses hoge.vfpre10 compressed by LZD VF(Prefix Base) with code size = 10, and output to fuga.vfpre10.

$ out/lzdDecompress -f hoge.vfpre10 -o fuga.vfpre10 -a vfpre

References

The detail of the algorithm was described in the following paper.

Keisuke Goto, Hideo Bannai, Shunsuke Inenaga and Masayuki Takeda. LZD Factorization: Simple and Practical Online Grammar Compression with Variable-to-Fixed Encoding, In Proceedings of the 26th Annual Symposium on Combinatorial Pattern Matching

License

Copyright © 2015 Keisuke Goto. This software released under the MIT License.

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LZ Double factor Factorization.

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