Editing LZMA (section)

== 7-Zip reference implementation ==
The LZMA implementation extracted from [[7-Zip]] is available as LZMA SDK. It was originally dual-licensed under both the [[GNU Lesser General Public License|GNU LGPL]] and [[Common Public License]],<ref>{{cite web | url = http://sourceforge.net/projects/sevenzip/files/LZMA%20SDK/4.23/ | title = Browse /LZMA SDK/4.23 | access-date = 2014-02-12 | publisher = [[SourceForge]]}}</ref> with an additional special exception for linked binaries, but was placed by [[Igor Pavlov (programmer)|Igor Pavlov]] in the [[public domain]] on December 2, 2008, with the release of version 4.62.<ref name="LZMA_SDK"/>

LZMA2 compression, which is an improved version of LZMA,<ref>{{cite web
| url=http://www.jrsoftware.org/ishelp/index.php?topic=setup_compression
| title=Inno Setup Help
| quote=LZMA2 is a modified version of LZMA that offers a better compression ratio for uncompressible data (random data expands about 0.005%, compared to 1.35% with original LZMA), and optionally can compress multiple parts of large files in parallel, greatly increasing compression speed but with a possible reduction in compression ratio.
| publisher=jrsoftware.org
| access-date=2013-06-16}}</ref> is now the default compression method for the .7z format, starting with version 9.30 on October 26, 2012.<ref>{{cite web
| url=http://www.7-zip.org/history.txt
| title=HISTORY of the 7-Zip
| date=2012-10-26
| access-date=2013-06-16
}}</ref>

The reference [[Open-source license|open source]] LZMA compression library was originally written in [[C++]] but has been ported to [[C (programming language)|ANSI C]], [[C Sharp (programming language)|C#]], and [[Java (programming language)|Java]].<ref name="LZMA_SDK" /> There are also third-party [[Python (programming language)|Python]] bindings for the C++ library,<ref>{{cite web
| url=http://www.joachim-bauch.de/projects/pylzma/
| title=PyLZMA – Platform independent python bindings for the LZMA compression library.
| first=Joachim
| last=Bauch
| date=2010-04-07
| access-date=2013-06-16}}</ref> as well as ports of LZMA to [[Pascal (programming language)|Pascal]],<ref>{{cite web
| url=http://www.birtles.org.uk/programming
| title=Programming Help: Pascal LZMA SDK
| date=2006-06-13
| first=Alan
| last=Birtles
| access-date=2013-06-16
}}</ref> [[Go (programming language)|Go]]<ref>
{{cite web
 |url          = http://lzma.googlecode.com/
 |archive-url  = http://webarchive.loc.gov/all/20160921065754/http://lzma.googlecode.com/
 |url-status   = dead
 |archive-date = 2016-09-21
 |title        = compress/lzma package for Go 1
 |first        = Andrei
 |last         = Vieru
 |date         = 2012-06-28
 |access-date   = 2013-06-16
}}</ref> and [[Ada (programming language)|Ada]].<ref>{{cite web
| url=http://unzip-ada.sourceforge.net/
| title=Zip-Ada}}</ref>

The 7-Zip implementation uses several variants of [[hash chain]]s, [[binary tree]]s and [[Patricia tree]]s as the basis for its dictionary search algorithm.

In addition to LZMA, the SDK and 7-Zip also implements multiple [[7z#Pre-processing filters|preprocessing filter]]s intended to improve compression, ranging from simple [[delta encoding]] (for images) and BCJ for executable code. It also provides some other compression algorithms used in 7z.

Decompression-only code for LZMA generally compiles to around 5&nbsp;KB, and the amount of RAM required during decompression is principally determined by the size of the [[sliding window]] used during compression. Small code size and relatively low memory overhead, particularly with smaller dictionary lengths, and free source code make the LZMA decompression algorithm well-suited to [[Embedded system|embedded]] applications.