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Merge commit 'c0cd028912e0be1386fca1fd6bb4e6324047e763' as 'Sources/LZ4'
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Sergey Abramchuk
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LZ4 - Extremely fast compression
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================================
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LZ4 is lossless compression algorithm,
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providing compression speed > 500 MB/s per core,
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scalable with multi-cores CPU.
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It features an extremely fast decoder,
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with speed in multiple GB/s per core,
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typically reaching RAM speed limits on multi-core systems.
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Speed can be tuned dynamically, selecting an "acceleration" factor
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which trades compression ratio for faster speed.
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On the other end, a high compression derivative, LZ4_HC, is also provided,
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trading CPU time for improved compression ratio.
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All versions feature the same decompression speed.
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LZ4 is also compatible with [dictionary compression](https://github.com/facebook/zstd#the-case-for-small-data-compression),
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and can ingest any input file as dictionary,
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including those created by [Zstandard Dictionary Builder](https://github.com/facebook/zstd/blob/v1.3.5/programs/zstd.1.md#dictionary-builder).
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(note: only the final 64KB are used).
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LZ4 library is provided as open-source software using BSD 2-Clause license.
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|Branch |Status |
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|------------|---------|
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|master | [![Build Status][travisMasterBadge]][travisLink] [![Build status][AppveyorMasterBadge]][AppveyorLink] [![coverity][coverBadge]][coverlink] |
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|dev | [![Build Status][travisDevBadge]][travisLink] [![Build status][AppveyorDevBadge]][AppveyorLink] |
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[travisMasterBadge]: https://travis-ci.org/lz4/lz4.svg?branch=master "Continuous Integration test suite"
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[travisDevBadge]: https://travis-ci.org/lz4/lz4.svg?branch=dev "Continuous Integration test suite"
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[travisLink]: https://travis-ci.org/lz4/lz4
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[AppveyorMasterBadge]: https://ci.appveyor.com/api/projects/status/github/lz4/lz4?branch=master&svg=true "Windows test suite"
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[AppveyorDevBadge]: https://ci.appveyor.com/api/projects/status/github/lz4/lz4?branch=dev&svg=true "Windows test suite"
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[AppveyorLink]: https://ci.appveyor.com/project/YannCollet/lz4-1lndh
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[coverBadge]: https://scan.coverity.com/projects/4735/badge.svg "Static code analysis of Master branch"
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[coverlink]: https://scan.coverity.com/projects/4735
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> **Branch Policy:**
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> - The "master" branch is considered stable, at all times.
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> - The "dev" branch is the one where all contributions must be merged
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before being promoted to master.
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> + If you plan to propose a patch, please commit into the "dev" branch,
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or its own feature branch.
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Direct commit to "master" are not permitted.
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Benchmarks
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-------------------------
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The benchmark uses [lzbench], from @inikep
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compiled with GCC v7.3.0 on Linux 64-bits (Debian 4.15.17-1).
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The reference system uses a Core i7-6700K CPU @ 4.0GHz.
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Benchmark evaluates the compression of reference [Silesia Corpus]
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in single-thread mode.
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[lzbench]: https://github.com/inikep/lzbench
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[Silesia Corpus]: http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia
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| Compressor | Ratio | Compression | Decompression |
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| ---------- | ----- | ----------- | ------------- |
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| memcpy | 1.000 |13100 MB/s | 13100 MB/s |
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|**LZ4 default (v1.8.2)** |**2.101**|**730 MB/s** | **3900 MB/s** |
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| LZO 2.09 | 2.108 | 630 MB/s | 800 MB/s |
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| QuickLZ 1.5.0 | 2.238 | 530 MB/s | 720 MB/s |
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| Snappy 1.1.4 | 2.091 | 525 MB/s | 1750 MB/s |
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| [Zstandard] 1.3.4 -1 | 2.877 | 470 MB/s | 1380 MB/s |
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| LZF v3.6 | 2.073 | 380 MB/s | 840 MB/s |
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| [zlib] deflate 1.2.11 -1| 2.730 | 100 MB/s | 380 MB/s |
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|**LZ4 HC -9 (v1.8.2)** |**2.721**| 40 MB/s | **3920 MB/s** |
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| [zlib] deflate 1.2.11 -6| 3.099 | 34 MB/s | 410 MB/s |
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[zlib]: http://www.zlib.net/
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[Zstandard]: http://www.zstd.net/
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LZ4 is also compatible and optimized for x32 mode,
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for which it provides additional speed performance.
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Installation
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-------------------------
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```
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make
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make install # this command may require root permissions
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```
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LZ4's `Makefile` supports standard [Makefile conventions],
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including [staged installs], [redirection], or [command redefinition].
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It is compatible with parallel builds (`-j#`).
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[Makefile conventions]: https://www.gnu.org/prep/standards/html_node/Makefile-Conventions.html
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[staged installs]: https://www.gnu.org/prep/standards/html_node/DESTDIR.html
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[redirection]: https://www.gnu.org/prep/standards/html_node/Directory-Variables.html
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[command redefinition]: https://www.gnu.org/prep/standards/html_node/Utilities-in-Makefiles.html
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Documentation
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-------------------------
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The raw LZ4 block compression format is detailed within [lz4_Block_format].
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Arbitrarily long files or data streams are compressed using multiple blocks,
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for streaming requirements. These blocks are organized into a frame,
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defined into [lz4_Frame_format].
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Interoperable versions of LZ4 must also respect the frame format.
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[lz4_Block_format]: doc/lz4_Block_format.md
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[lz4_Frame_format]: doc/lz4_Frame_format.md
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Other source versions
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-------------------------
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Beyond the C reference source,
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many contributors have created versions of lz4 in multiple languages
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(Java, C#, Python, Perl, Ruby, etc.).
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A list of known source ports is maintained on the [LZ4 Homepage].
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[LZ4 Homepage]: http://www.lz4.org
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