Lempel–Ziv–Oberhumer (LZO) is a

lossless Lossless compression is a class of data compression that allows the original data to be perfectly reconstructed from the compressed data with no loss of information. Lossless compression is possible because most real-world data exhibits statisti ...

data compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compressi ...

algorithm In mathematics and computer science, an algorithm () is a finite sequence of Rigour#Mathematics, mathematically rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algo ...

that is focused on decompression speed.

Design

The original "lzop" implementation, released in 1996, was developed by Markus Franz Xaver Johannes Oberhumer, based on earlier algorithms by Abraham Lempel and Jacob Ziv. The LZO library implements a number of algorithms with the following characteristics: * Higher compression speed compared to DEFLATE compression * Very fast decompression * Requires an additional buffer during compression (of size 8 kB or 64 kB, depending on compression level) * Requires no additional memory for decompression other than the source and destination buffers * Allows the user to adjust the balance between compression ratio and compression speed, without affecting the speed of decompression LZO supports overlapping compression and in-place decompression. As a block compression algorithm, it compresses and decompresses blocks of data. Block size must be the same for compression and decompression. LZO compresses a block of data into ''matches'' (a sliding dictionary) and ''runs'' of non-matching literals to produce good results on highly redundant data and deals acceptably with non-compressible data, only expanding incompressible data by a maximum of 1/64 of the original size when measured over a block size of at least 1 kB.

Implementations

The reference implementation is written in

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, and it has been made available as

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under the

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. The

copyright A copyright is a type of intellectual property that gives its owner the exclusive legal right to copy, distribute, adapt, display, and perform a creative work, usually for a limited time. The creative work may be in a literary, artistic, ...

for the code is owned by Markus F. X. J. Oberhumer. It was originally published in 1996. Oberhumer has also written a command-line frontend called lzop. Versions of LZO are available for the

Perl Perl is a high-level, general-purpose, interpreted, dynamic programming language. Though Perl is not officially an acronym, there are various backronyms in use, including "Practical Extraction and Reporting Language". Perl was developed ...

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and

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languages. Various LZO implementations are reported to work under

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(Atari ST), ConvexOS,

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Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

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, and

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. FFmpeg's libavutil library includes its own implementation of LZO as a possible method for lossless video compression. FFmpeg's implementation of the decompressor is also used in OpenConnect in order to support LZO-compressed ESP packets sent by

Juniper Networks Juniper Networks, Inc. is an American multinational corporation headquartered in Sunnyvale, California. The company develops and markets networking products, including Router (computing), routers, Network switch, switches, network management so ...

and

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VPN servers. The Linux kernel uses its LZO implementation in some of its features: *

btrfs Btrfs (pronounced as "better F S", "butter F S", "b-tree F S", or "B.T.R.F.S.") is a computer storage format that combines a file system based on the copy-on-write (COW) principle with a logical volume manager (distinct from Linux's LVM), d ...

uses LZO as a possible compression method for file system compression. * initrd and initramfs use LZO as a possible compression method for initial

RAM drive A RAM drive (also called a RAM disk) is a block of random-access memory (primary storage or volatile memory) that a computer's software is treating as if the memory were a disk drive (secondary storage). RAM drives provide high-performance tempo ...

compression. *

SquashFS Squashfs is a compressed read-only file system for Linux. Squashfs compresses files, inodes and directories, and supports block sizes from 4 KiB up to 1 MiB for greater compression. Several compression algorithms are supported. Squashfs is ...

uses LZO as a possible compression method for file system compression. * zram uses LZO with

run-length encoding Run-length encoding (RLE) is a form of lossless data compression in which ''runs'' of data (consecutive occurrences of the same data value) are stored as a single occurrence of that data value and a count of its consecutive occurrences, rather th ...

called LZO-RLE as the default compression method for

compression. *

zswap zswap is a Linux kernel feature that provides a compressed write-back Cache (computing), cache for Paging, swapped pages, as a form of virtual memory compression. Instead of moving memory pages to a swap device when they are to be swapped ou ...

uses LZO as the default compression method for virtual memory compression

References

External links

* * - Pure Java implementation of the liblzo2 LZO compression algorithm {{DEFAULTSORT:Lempel-Ziv-Oberhumer Lossless compression algorithms Free data compression software C (programming language) libraries Data compression