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source-engine/utils/lzma/DOC/lzma-sdk.txt
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LZMA SDK 9.38
-------------
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)
You can copy, modify, distribute and perform LZMA SDK code, even for commercial purposes,
all without asking permission.
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
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