gzdoom-gles/libraries/lzma/DOC/lzma-sdk.txt

LZMA SDK 19.00
--------------

LZMA SDK provides the documentation, samples, header files,
libraries, and tools you need to develop applications that 
use 7z / LZMA / LZMA2 / XZ compression.

LZMA is an improved version of famous LZ77 compression algorithm. 
It was improved in way of maximum increasing of compression ratio,
keeping high decompression speed and low memory requirements for 
decompressing.

LZMA2 is a LZMA based compression method. LZMA2 provides better 
multithreading support for compression than LZMA and some other improvements.

7z is a file format for data compression and file archiving.
7z is a main file format for 7-Zip compression program (www.7-zip.org).
7z format supports different compression methods: LZMA, LZMA2 and others.
7z also supports AES-256 based encryption.

XZ is a file format for data compression that uses LZMA2 compression.
XZ format provides additional features: SHA/CRC check, filters for 
improved compression ratio, splitting to blocks and streams,



LICENSE
-------

LZMA SDK is written and placed in the public domain by Igor Pavlov.

Some code in LZMA SDK is based on public domain code from another developers:
  1) PPMd var.H (2001): Dmitry Shkarin
  2) SHA-256: Wei Dai (Crypto++ library)

Anyone is free to copy, modify, publish, use, compile, sell, or distribute the 
original LZMA SDK code, either in source code form or as a compiled binary, for 
any purpose, commercial or non-commercial, and by any means.

LZMA SDK code is compatible with open source licenses, for example, you can 
include it to GNU GPL or GNU LGPL code.


LZMA SDK Contents
-----------------

  Source code:

    - C / C++ / C# / Java   - LZMA compression and decompression
    - C / C++               - LZMA2 compression and decompression
    - C / C++               - XZ compression and decompression
    - C                     - 7z decompression
    -     C++               - 7z compression and decompression
    - C                     - small SFXs for installers (7z decompression)
    -     C++               - SFXs and SFXs for installers (7z decompression)

  Precomiled binaries:

    - console programs for lzma / 7z / xz compression and decompression
    - SFX modules for installers.


UNIX/Linux version 
------------------
To compile C++ version of file->file LZMA encoding, go to directory
CPP/7zip/Bundles/LzmaCon
and call make to recompile it:
  make -f makefile.gcc clean all

In some UNIX/Linux versions you must compile LZMA with static libraries.
To compile with static libraries, you can use 
LIB = -lm -static

Also you can use p7zip (port of 7-Zip for POSIX systems like Unix or Linux):
  
  http://p7zip.sourceforge.net/


Files
-----

DOC/7zC.txt          - 7z ANSI-C Decoder description
DOC/7zFormat.txt     - 7z Format description
DOC/installer.txt    - information about 7-Zip for installers
DOC/lzma.txt         - LZMA compression description
DOC/lzma-sdk.txt     - LZMA SDK description (this file)
DOC/lzma-history.txt - history of LZMA SDK
DOC/lzma-specification.txt - Specification of LZMA
DOC/Methods.txt      - Compression method IDs for .7z

bin/installer/   - example script to create installer that uses SFX module,

bin/7zdec.exe    - simplified 7z archive decoder
bin/7zr.exe      - 7-Zip console program (reduced version)
bin/x64/7zr.exe  - 7-Zip console program (reduced version) (x64 version)
bin/lzma.exe     - file->file LZMA encoder/decoder for Windows
bin/7zS2.sfx     - small SFX module for installers (GUI version)
bin/7zS2con.sfx  - small SFX module for installers (Console version)
bin/7zSD.sfx     - SFX module for installers.


7zDec.exe
---------
7zDec.exe is simplified 7z archive decoder.
It supports only LZMA, LZMA2, and PPMd methods.
7zDec decodes whole solid block from 7z archive to RAM.
The RAM consumption can be high.




Source code structure
---------------------


Asm/ - asm files (optimized code for CRC calculation and Intel-AES encryption)

C/  - C files (compression / decompression and other)
  Util/
    7z       - 7z decoder program (decoding 7z files)
    Lzma     - LZMA program (file->file LZMA encoder/decoder).
    LzmaLib  - LZMA library (.DLL for Windows)
    SfxSetup - small SFX module for installers 

CPP/ -- CPP files

  Common  - common files for C++ projects
  Windows - common files for Windows related code

  7zip    - files related to 7-Zip

    Archive - files related to archiving

      Common   - common files for archive handling
      7z       - 7z C++ Encoder/Decoder

    Bundles  - Modules that are bundles of other modules (files)
  
      Alone7z       - 7zr.exe: Standalone 7-Zip console program (reduced version)
      Format7zExtractR  - 7zxr.dll: Reduced version of 7z DLL: extracting from 7z/LZMA/BCJ/BCJ2.
      Format7zR         - 7zr.dll:  Reduced version of 7z DLL: extracting/compressing to 7z/LZMA/BCJ/BCJ2
      LzmaCon       - lzma.exe: LZMA compression/decompression
      LzmaSpec      - example code for LZMA Specification
      SFXCon        - 7zCon.sfx: Console 7z SFX module
      SFXSetup      - 7zS.sfx: 7z SFX module for installers
      SFXWin        - 7z.sfx: GUI 7z SFX module

    Common   - common files for 7-Zip

    Compress - files for compression/decompression

    Crypto   - files for encryption / decompression

    UI       - User Interface files
         
      Client7z - Test application for 7za.dll, 7zr.dll, 7zxr.dll
      Common   - Common UI files
      Console  - Code for console program (7z.exe)
      Explorer    - Some code from 7-Zip Shell extension
      FileManager - Some GUI code from 7-Zip File Manager
      GUI         - Some GUI code from 7-Zip


CS/ - C# files
  7zip
    Common   - some common files for 7-Zip
    Compress - files related to compression/decompression
      LZ     - files related to LZ (Lempel-Ziv) compression algorithm
      LZMA         - LZMA compression/decompression
      LzmaAlone    - file->file LZMA compression/decompression
      RangeCoder   - Range Coder (special code of compression/decompression)

Java/  - Java files
  SevenZip
    Compression    - files related to compression/decompression
      LZ           - files related to LZ (Lempel-Ziv) compression algorithm
      LZMA         - LZMA compression/decompression
      RangeCoder   - Range Coder (special code of compression/decompression)


Note: 
  Asm / C / C++ source code of LZMA SDK is part of 7-Zip's source code.
  7-Zip's source code can be downloaded from 7-Zip's SourceForge page:

  http://sourceforge.net/projects/sevenzip/



LZMA features
-------------
  - Variable dictionary size (up to 1 GB)
  - Estimated compressing speed: about 2 MB/s on 2 GHz CPU
  - Estimated decompressing speed: 
      - 20-30 MB/s on modern 2 GHz cpu
      - 1-2 MB/s on 200 MHz simple RISC cpu: (ARM, MIPS, PowerPC)
  - Small memory requirements for decompressing (16 KB + DictionarySize)
  - Small code size for decompressing: 5-8 KB

LZMA decoder uses only integer operations and can be 
implemented in any modern 32-bit CPU (or on 16-bit CPU with some conditions).

Some critical operations that affect the speed of LZMA decompression:
  1) 32*16 bit integer multiply
  2) Mispredicted branches (penalty mostly depends from pipeline length)
  3) 32-bit shift and arithmetic operations

The speed of LZMA decompressing mostly depends from CPU speed.
Memory speed has no big meaning. But if your CPU has small data cache, 
overall weight of memory speed will slightly increase.


How To Use
----------

Using LZMA encoder/decoder executable
--------------------------------------

Usage:  LZMA <e|d> inputFile outputFile [<switches>...]

  e: encode file

  d: decode file

  b: Benchmark. There are two tests: compressing and decompressing 
     with LZMA method. Benchmark shows rating in MIPS (million 
     instructions per second). Rating value is calculated from 
     measured speed and it is normalized with Intel's Core 2 results.
     Also Benchmark checks possible hardware errors (RAM 
     errors in most cases). Benchmark uses these settings:
     (-a1, -d21, -fb32, -mfbt4). You can change only -d parameter. 
     Also you can change the number of iterations. Example for 30 iterations:
       LZMA b 30
     Default number of iterations is 10.

<Switches>
  

  -a{N}:  set compression mode 0 = fast, 1 = normal
          default: 1 (normal)

  d{N}:   Sets Dictionary size - [0, 30], default: 23 (8MB)
          The maximum value for dictionary size is 1 GB = 2^30 bytes.
          Dictionary size is calculated as DictionarySize = 2^N bytes. 
          For decompressing file compressed by LZMA method with dictionary 
          size D = 2^N you need about D bytes of memory (RAM).

  -fb{N}: set number of fast bytes - [5, 273], default: 128
          Usually big number gives a little bit better compression ratio 
          and slower compression process.

  -lc{N}: set number of literal context bits - [0, 8], default: 3
          Sometimes lc=4 gives gain for big files.

  -lp{N}: set number of literal pos bits - [0, 4], default: 0
          lp switch is intended for periodical data when period is 
          equal 2^N. For example, for 32-bit (4 bytes) 
          periodical data you can use lp=2. Often it's better to set lc0, 
          if you change lp switch.

  -pb{N}: set number of pos bits - [0, 4], default: 2
          pb switch is intended for periodical data 
          when period is equal 2^N.

  -mf{MF_ID}: set Match Finder. Default: bt4. 
              Algorithms from hc* group doesn't provide good compression 
              ratio, but they often works pretty fast in combination with 
              fast mode (-a0).

              Memory requirements depend from dictionary size 
              (parameter "d" in table below). 

               MF_ID     Memory                   Description

                bt2    d *  9.5 + 4MB  Binary Tree with 2 bytes hashing.
                bt3    d * 11.5 + 4MB  Binary Tree with 3 bytes hashing.
                bt4    d * 11.5 + 4MB  Binary Tree with 4 bytes hashing.
                hc4    d *  7.5 + 4MB  Hash Chain with 4 bytes hashing.

  -eos:   write End Of Stream marker. By default LZMA doesn't write 
          eos marker, since LZMA decoder knows uncompressed size 
          stored in .lzma file header.

  -si:    Read data from stdin (it will write End Of Stream marker).
  -so:    Write data to stdout


Examples:

1) LZMA e file.bin file.lzma -d16 -lc0 

compresses file.bin to file.lzma with 64 KB dictionary (2^16=64K)  
and 0 literal context bits. -lc0 allows to reduce memory requirements 
for decompression.


2) LZMA e file.bin file.lzma -lc0 -lp2

compresses file.bin to file.lzma with settings suitable 
for 32-bit periodical data (for example, ARM or MIPS code).

3) LZMA d file.lzma file.bin

decompresses file.lzma to file.bin.


Compression ratio hints
-----------------------

Recommendations
---------------

To increase the compression ratio for LZMA compressing it's desirable 
to have aligned data (if it's possible) and also it's desirable to locate
data in such order, where code is grouped in one place and data is 
grouped in other place (it's better than such mixing: code, data, code,
data, ...).


Filters
-------
You can increase the compression ratio for some data types, using
special filters before compressing. For example, it's possible to 
increase the compression ratio on 5-10% for code for those CPU ISAs: 
x86, IA-64, ARM, ARM-Thumb, PowerPC, SPARC.

You can find C source code of such filters in C/Bra*.* files

You can check the compression ratio gain of these filters with such 
7-Zip commands (example for ARM code):
No filter:
  7z a a1.7z a.bin -m0=lzma

With filter for little-endian ARM code:
  7z a a2.7z a.bin -m0=arm -m1=lzma        

It works in such manner:
Compressing    = Filter_encoding + LZMA_encoding
Decompressing  = LZMA_decoding + Filter_decoding

Compressing and decompressing speed of such filters is very high,
so it will not increase decompressing time too much.
Moreover, it reduces decompression time for LZMA_decoding, 
since compression ratio with filtering is higher.

These filters convert CALL (calling procedure) instructions 
from relative offsets to absolute addresses, so such data becomes more 
compressible.

For some ISAs (for example, for MIPS) it's impossible to get gain from such filter.



---

http://www.7-zip.org
http://www.7-zip.org/sdk.html
http://www.7-zip.org/support.html