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357 lines
12 KiB
Text
357 lines
12 KiB
Text
LZMA SDK 19.00
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--------------
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LZMA SDK provides the documentation, samples, header files,
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libraries, and tools you need to develop applications that
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use 7z / LZMA / LZMA2 / XZ compression.
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LZMA is an improved version of famous LZ77 compression algorithm.
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It was improved in way of maximum increasing of compression ratio,
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keeping high decompression speed and low memory requirements for
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decompressing.
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LZMA2 is a LZMA based compression method. LZMA2 provides better
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multithreading support for compression than LZMA and some other improvements.
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7z is a file format for data compression and file archiving.
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7z is a main file format for 7-Zip compression program (www.7-zip.org).
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7z format supports different compression methods: LZMA, LZMA2 and others.
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7z also supports AES-256 based encryption.
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XZ is a file format for data compression that uses LZMA2 compression.
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XZ format provides additional features: SHA/CRC check, filters for
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improved compression ratio, splitting to blocks and streams,
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LICENSE
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-------
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LZMA SDK is written and placed in the public domain by Igor Pavlov.
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Some code in LZMA SDK is based on public domain code from another developers:
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1) PPMd var.H (2001): Dmitry Shkarin
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2) SHA-256: Wei Dai (Crypto++ library)
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Anyone is free to copy, modify, publish, use, compile, sell, or distribute the
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original LZMA SDK code, either in source code form or as a compiled binary, for
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any purpose, commercial or non-commercial, and by any means.
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LZMA SDK code is compatible with open source licenses, for example, you can
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include it to GNU GPL or GNU LGPL code.
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LZMA SDK Contents
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-----------------
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Source code:
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- C / C++ / C# / Java - LZMA compression and decompression
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- C / C++ - LZMA2 compression and decompression
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- C / C++ - XZ compression and decompression
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- C - 7z decompression
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- C++ - 7z compression and decompression
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- C - small SFXs for installers (7z decompression)
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- C++ - SFXs and SFXs for installers (7z decompression)
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Precomiled binaries:
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- console programs for lzma / 7z / xz compression and decompression
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- SFX modules for installers.
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UNIX/Linux version
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------------------
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To compile C++ version of file->file LZMA encoding, go to directory
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CPP/7zip/Bundles/LzmaCon
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and call make to recompile it:
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make -f makefile.gcc clean all
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In some UNIX/Linux versions you must compile LZMA with static libraries.
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To compile with static libraries, you can use
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LIB = -lm -static
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Also you can use p7zip (port of 7-Zip for POSIX systems like Unix or Linux):
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http://p7zip.sourceforge.net/
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Files
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-----
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DOC/7zC.txt - 7z ANSI-C Decoder description
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DOC/7zFormat.txt - 7z Format description
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DOC/installer.txt - information about 7-Zip for installers
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DOC/lzma.txt - LZMA compression description
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DOC/lzma-sdk.txt - LZMA SDK description (this file)
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DOC/lzma-history.txt - history of LZMA SDK
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DOC/lzma-specification.txt - Specification of LZMA
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DOC/Methods.txt - Compression method IDs for .7z
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bin/installer/ - example script to create installer that uses SFX module,
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bin/7zdec.exe - simplified 7z archive decoder
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bin/7zr.exe - 7-Zip console program (reduced version)
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bin/x64/7zr.exe - 7-Zip console program (reduced version) (x64 version)
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bin/lzma.exe - file->file LZMA encoder/decoder for Windows
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bin/7zS2.sfx - small SFX module for installers (GUI version)
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bin/7zS2con.sfx - small SFX module for installers (Console version)
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bin/7zSD.sfx - SFX module for installers.
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7zDec.exe
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---------
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7zDec.exe is simplified 7z archive decoder.
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It supports only LZMA, LZMA2, and PPMd methods.
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7zDec decodes whole solid block from 7z archive to RAM.
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The RAM consumption can be high.
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Source code structure
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---------------------
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Asm/ - asm files (optimized code for CRC calculation and Intel-AES encryption)
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C/ - C files (compression / decompression and other)
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Util/
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7z - 7z decoder program (decoding 7z files)
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Lzma - LZMA program (file->file LZMA encoder/decoder).
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LzmaLib - LZMA library (.DLL for Windows)
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SfxSetup - small SFX module for installers
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CPP/ -- CPP files
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Common - common files for C++ projects
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Windows - common files for Windows related code
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7zip - files related to 7-Zip
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Archive - files related to archiving
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Common - common files for archive handling
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7z - 7z C++ Encoder/Decoder
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Bundles - Modules that are bundles of other modules (files)
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Alone7z - 7zr.exe: Standalone 7-Zip console program (reduced version)
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Format7zExtractR - 7zxr.dll: Reduced version of 7z DLL: extracting from 7z/LZMA/BCJ/BCJ2.
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Format7zR - 7zr.dll: Reduced version of 7z DLL: extracting/compressing to 7z/LZMA/BCJ/BCJ2
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LzmaCon - lzma.exe: LZMA compression/decompression
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LzmaSpec - example code for LZMA Specification
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SFXCon - 7zCon.sfx: Console 7z SFX module
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SFXSetup - 7zS.sfx: 7z SFX module for installers
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SFXWin - 7z.sfx: GUI 7z SFX module
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Common - common files for 7-Zip
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Compress - files for compression/decompression
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Crypto - files for encryption / decompression
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UI - User Interface files
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Client7z - Test application for 7za.dll, 7zr.dll, 7zxr.dll
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Common - Common UI files
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Console - Code for console program (7z.exe)
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Explorer - Some code from 7-Zip Shell extension
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FileManager - Some GUI code from 7-Zip File Manager
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GUI - Some GUI code from 7-Zip
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CS/ - C# files
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7zip
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Common - some common files for 7-Zip
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Compress - files related to compression/decompression
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LZ - files related to LZ (Lempel-Ziv) compression algorithm
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LZMA - LZMA compression/decompression
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LzmaAlone - file->file LZMA compression/decompression
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RangeCoder - Range Coder (special code of compression/decompression)
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Java/ - Java files
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SevenZip
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Compression - files related to compression/decompression
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LZ - files related to LZ (Lempel-Ziv) compression algorithm
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LZMA - LZMA compression/decompression
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RangeCoder - Range Coder (special code of compression/decompression)
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Note:
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Asm / C / C++ source code of LZMA SDK is part of 7-Zip's source code.
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7-Zip's source code can be downloaded from 7-Zip's SourceForge page:
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http://sourceforge.net/projects/sevenzip/
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LZMA features
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-------------
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- Variable dictionary size (up to 1 GB)
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- Estimated compressing speed: about 2 MB/s on 2 GHz CPU
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- Estimated decompressing speed:
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- 20-30 MB/s on modern 2 GHz cpu
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- 1-2 MB/s on 200 MHz simple RISC cpu: (ARM, MIPS, PowerPC)
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- Small memory requirements for decompressing (16 KB + DictionarySize)
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- Small code size for decompressing: 5-8 KB
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LZMA decoder uses only integer operations and can be
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implemented in any modern 32-bit CPU (or on 16-bit CPU with some conditions).
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Some critical operations that affect the speed of LZMA decompression:
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1) 32*16 bit integer multiply
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2) Mispredicted branches (penalty mostly depends from pipeline length)
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3) 32-bit shift and arithmetic operations
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The speed of LZMA decompressing mostly depends from CPU speed.
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Memory speed has no big meaning. But if your CPU has small data cache,
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overall weight of memory speed will slightly increase.
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How To Use
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----------
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Using LZMA encoder/decoder executable
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--------------------------------------
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Usage: LZMA <e|d> inputFile outputFile [<switches>...]
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e: encode file
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d: decode file
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b: Benchmark. There are two tests: compressing and decompressing
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with LZMA method. Benchmark shows rating in MIPS (million
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instructions per second). Rating value is calculated from
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measured speed and it is normalized with Intel's Core 2 results.
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Also Benchmark checks possible hardware errors (RAM
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errors in most cases). Benchmark uses these settings:
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(-a1, -d21, -fb32, -mfbt4). You can change only -d parameter.
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Also you can change the number of iterations. Example for 30 iterations:
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LZMA b 30
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Default number of iterations is 10.
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<Switches>
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-a{N}: set compression mode 0 = fast, 1 = normal
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default: 1 (normal)
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d{N}: Sets Dictionary size - [0, 30], default: 23 (8MB)
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The maximum value for dictionary size is 1 GB = 2^30 bytes.
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Dictionary size is calculated as DictionarySize = 2^N bytes.
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For decompressing file compressed by LZMA method with dictionary
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size D = 2^N you need about D bytes of memory (RAM).
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-fb{N}: set number of fast bytes - [5, 273], default: 128
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Usually big number gives a little bit better compression ratio
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and slower compression process.
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-lc{N}: set number of literal context bits - [0, 8], default: 3
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Sometimes lc=4 gives gain for big files.
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-lp{N}: set number of literal pos bits - [0, 4], default: 0
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lp switch is intended for periodical data when period is
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equal 2^N. For example, for 32-bit (4 bytes)
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periodical data you can use lp=2. Often it's better to set lc0,
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if you change lp switch.
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-pb{N}: set number of pos bits - [0, 4], default: 2
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pb switch is intended for periodical data
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when period is equal 2^N.
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-mf{MF_ID}: set Match Finder. Default: bt4.
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Algorithms from hc* group doesn't provide good compression
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ratio, but they often works pretty fast in combination with
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fast mode (-a0).
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Memory requirements depend from dictionary size
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(parameter "d" in table below).
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MF_ID Memory Description
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bt2 d * 9.5 + 4MB Binary Tree with 2 bytes hashing.
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bt3 d * 11.5 + 4MB Binary Tree with 3 bytes hashing.
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bt4 d * 11.5 + 4MB Binary Tree with 4 bytes hashing.
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hc4 d * 7.5 + 4MB Hash Chain with 4 bytes hashing.
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-eos: write End Of Stream marker. By default LZMA doesn't write
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eos marker, since LZMA decoder knows uncompressed size
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stored in .lzma file header.
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-si: Read data from stdin (it will write End Of Stream marker).
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-so: Write data to stdout
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Examples:
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1) LZMA e file.bin file.lzma -d16 -lc0
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compresses file.bin to file.lzma with 64 KB dictionary (2^16=64K)
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and 0 literal context bits. -lc0 allows to reduce memory requirements
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for decompression.
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2) LZMA e file.bin file.lzma -lc0 -lp2
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compresses file.bin to file.lzma with settings suitable
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for 32-bit periodical data (for example, ARM or MIPS code).
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3) LZMA d file.lzma file.bin
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decompresses file.lzma to file.bin.
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Compression ratio hints
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-----------------------
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Recommendations
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---------------
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To increase the compression ratio for LZMA compressing it's desirable
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to have aligned data (if it's possible) and also it's desirable to locate
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data in such order, where code is grouped in one place and data is
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grouped in other place (it's better than such mixing: code, data, code,
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data, ...).
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Filters
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-------
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You can increase the compression ratio for some data types, using
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special filters before compressing. For example, it's possible to
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increase the compression ratio on 5-10% for code for those CPU ISAs:
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x86, IA-64, ARM, ARM-Thumb, PowerPC, SPARC.
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You can find C source code of such filters in C/Bra*.* files
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You can check the compression ratio gain of these filters with such
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7-Zip commands (example for ARM code):
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No filter:
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7z a a1.7z a.bin -m0=lzma
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With filter for little-endian ARM code:
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7z a a2.7z a.bin -m0=arm -m1=lzma
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It works in such manner:
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Compressing = Filter_encoding + LZMA_encoding
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Decompressing = LZMA_decoding + Filter_decoding
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Compressing and decompressing speed of such filters is very high,
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so it will not increase decompressing time too much.
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Moreover, it reduces decompression time for LZMA_decoding,
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since compression ratio with filtering is higher.
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These filters convert CALL (calling procedure) instructions
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from relative offsets to absolute addresses, so such data becomes more
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compressible.
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For some ISAs (for example, for MIPS) it's impossible to get gain from such filter.
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---
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http://www.7-zip.org
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http://www.7-zip.org/sdk.html
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http://www.7-zip.org/support.html
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