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https://github.com/hxim/paq8px

PAQ8PX compression archiver
https://github.com/hxim/paq8px

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PAQ8PX compression archiver

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README 

        


                              PAQ8PX README



---------

COPYRIGHT

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    Copyright (C) 2008 Matt Mahoney, Serge Osnach, Alexander Ratushnyak,

    Bill Pettis, Przemyslaw Skibinski, Matthew Fite, wowtiger, Andrew Paterson,

    Jan Ondrus, Andreas Morphis, Pavel L. Holoborodko, Kaido Orav, Simon Berger,

    Neill Corlett, Márcio Pais, Andrew Epstein, Mauro Vezzosi, Zoltán Gotthardt,

    Sebastian Lehmann, Moisés Cardona, Byron Knoll



    We would like to express our gratitude for the endless support of many 

    contributors who encouraged PAQ8PX development with ideas, testing, 

    compiling, debugging:

    LovePimple, Skymmer, Darek, Stephan Busch, m^2, Christian Schneider,

    pat357, Rugxulo, Gonzalo, a902cd23, pinguin2, Luca Biondi - and many others.



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LICENCE

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    This program is free software; you can redistribute it and/or

    modify it under the terms of the GNU General Public License as

    published by the Free Software Foundation; either version 2 of

    the License, or (at your option) any later version.



    This program is distributed in the hope that it will be useful, but

    WITHOUT ANY WARRANTY; without even the implied warranty of

    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    General Public License for more details at

    Visit .



    For a summary of your rights and obligations in plain language visit 

    https://tldrlegal.com/license/gnu-general-public-license-v2



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ABOUT

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PAQ is a series of experimental lossless data compression software that have gone 

through collaborative development to top rankings on several benchmarks measuring 

compression ratio (although at the expense of speed and memory usage).



PAQ8PX (this branch) is one of the longest living branch of the PAQ series started 

by Jan Ondrus in 2009.



PAQ8PX is suitable and recommended for file entropy estimation. However - being an 

experimental compressor - it is not recommended for production use or for file 

archival purposes.



For history and current state of development visit https://encode.su/threads/342-paq8px



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HOW DOES IT WORK?

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Data compression is carried out by compressing the input file(s) bit by bit using 

context mixing i.e. mixing predictions from many models. For a longer (technical) 

explanation see the DOC file.



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PAQ8PX ARCHIVES

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A PAQ8PX archive stores a file or multiple files in a highly compressed format.



You can recognize a PAQ8PX archive from its file extension. The file extension reflects 

the exact PAQ8PX version that created the archive. You may also examine the first few

bytes of the file. If it reads "paq8px" then it is (most probably) a PAQ8PX archive. 

Exact version information cannot be inferred from the archive content.



A PAQ8PX archive may contain multiple files, but once created, you cannot

add to or remove files from the archive.



In single file mode (i.e. when compressing just one file) only file contents are 

stored. File paths, file names, creation or modification dates, file attributes, 

permissions and other metadata are not preserved. In multiple file mode however, 

you may store such metadata in the archive (see the help screen for more details).



Notes on pre-training:

(1)

 The exe pre-training function (see the command line flag "e") uses the paq8px.exe 

 file itself to pre-train the exe prediction model, so expect the resulting archives 

 to be different created by two different paq8px.exe executables - even when built

 with the same command line options from the same source. When the exe is different, 

 the predictions will be slightly different, thus the archives will be (completely) 

 different. As a result you must have the very executable that created an archive in

 order to extract its contents when you use this pre-training option.

 

(2)

 If you use the text pre-training function (see the command line flag "t"), the 

 word list (english.dic) and expression list (english.exp) files are only used for 

 pre-training the prediction model before the actual file compression would begin.

 However their content is not stored in the archive. Since these files are required 

 to pre-train the model before decompression as well, you will need to have them

 when extracting files from your archive.



More notes:

Files and archives larger than 2 GB are not (yet) supported.

PAQ8PX archives are not compatible with previous or future PAQ8PX releases.



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HOW TO USE

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This software is portable, you don't need to install it.



You may copy paq8px.exe to the folder where your files to be compressed are located

and launch PAQ8PX from the command line (cmd.exe in Windows, a terminal of your choice 

in Linux, macOS and Android). 



----------------------

COMMAND LINE INTERFACE

----------------------



A graphical user interface is not provided, PAQ8PX runs from the command line.

See the help screen for command line options.

For the help screen just launch PAQ8PX from the command line without any options.



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SOURCE CODE

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https://github.com/hxim



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HOW TO COMPILE

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Building PAQ8PX requires a C++17 capable C++ compiler:

https://en.cppreference.com/w/cpp/compiler_support#cpp17



Windows 

If you are a Windows user you don't need to compile the source. Just grab the latest

executable from the https://encode.su/threads/342-paq8px thread.

If you would like to build an executable yourself you may use the Visual Studio solution

file or in case of Mingw-w64 see the "build-mingw-w64-generic-publish.cmd" batch file

in the build subfolder.



Linux/macOS

gcc/clang users on Linux/macOS may use the following commands to build:



 sudo apt-get install build-essential zlib1g-dev cmake make

 cd build

 cmake ..

 make



The following compilers were tested and verified to compile/work correctly

in this release or in an earlier release:



  - Visual Studio 2017 Community Edition (Windows)

  - Visual Studio 2019 Community Edition (Windows) verified @v207fix1

  - MinGW-w64 7.1.0 (Windows)

  - MinGW-w64 7.2.0 (Windows)

  - MinGW-w64 8.1.0 (Windows) verified @v187fix1

  - MinGW-w64 9.3.0 (Windows) verified @v207fix1

  - GCC 7.3.0 (macOS)

  - GCC 7.2.0 (Ubuntu)

  - GCC 8.3.0 (Lubuntu) verified @v187fix1

  - GCC 9.3.0 (Ubuntu) verified @v207fix1

  - clang 8.0.0-3 (Lubuntu) verified @v187fix1

  - clang 10.0.0-4 (ubuntu) verified @v207fix1

  - aarch64-linux-gnu-gcc 9.4.0 (Ubuntu) @v207fix1



Note:



 We build and test 64-bit releases, 32-bit releases are seldom built or tested. A known

 limitation of 32-bit releases is the 2 GB memory barrier. As a consequence, compression 

 and decompression with 32-bit releases may not work ("out of memory") on level 8 and above.

 

--------------

FOR DEVELOPERS

--------------



When you make a new release:



  - Please update the version number in the "Versioning" section in the paq8px.cpp source file.

  - Please append a short description of your modifications to the CHANGELOG file.

  - If you publish an executable, always publish a static build (link the required library files statically).

  - Always publish a build for the general public (e.g. don't use -march=native).

  - Before publishing your build, please carry out some basic tests. Run your tests

    with asserts on (remove the "NDEBUG" preprocessor directive).