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.

LZ-ABT

LZ-ABT is a new LZ78-style grammar compression algorithm which is a simple online algorithm to create. This can avoid the lower-bound time of the naive algorithms for LZD, other LZ78-style compression algorithms, which was observed in [Badkobeh et. al., SPIRE 2017, 51-67]

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/compress
Usage  : out/compress [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 lzd_ns             : LZD not using stream
  -a lzd                : LZD
  -a lzabt_ns           : LZABT_NS
  -a lzabt              : LZABT
  -a lzabt_comp         : LZABT in compressed space

Examples

The following command compresses SConstruct, and output to hoge.lz by the algorithm LZ-ABT.

$ out/compress -f SConstruct -o hoge.lz -a lzabt -p 0.2

Decompress

Usage

% out/lzdDecompress
Usage  : out/decompress [options]
Options                 : 
  -f FileName           : input file
  -o FileName           : output file
  -d NUM                : debug mode

To decode binary file encoded with 'out/comress' command, use 'out/decompress'

Examples

The following command decompresses hoge.lz and output to decoded.txt. All encoded files compressed by 'out/compress' have the same encode format

$ out/deecompress -f hoge.lz -o decoded.txt

References

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

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

Tatsuya Ohno, Keisuke Goto, Yoshimasa Takabatake, Tomohiro I and Hiroshi Sakamoto. LZ-ABT: A Practical Algorithm for \alpha-Balanced Grammar Compression, In Proceedings of the 29th International Workshop on Combinatorial Algorithms

License

Copyright (c) 2018 Tatsuya Ohno. This software released under the MIT License.