lz4/README.md

LZ4 - Extremely fast compression
================================

LZ4 is lossless compression algorithm,
providing compression speed > 500 MB/s per core,
scalable with multi-cores CPU.
It features an extremely fast decoder,
with speed in multiple GB/s per core,
typically reaching RAM speed limits on multi-core systems.

Speed can be tuned dynamically, selecting an "acceleration" factor
which trades compression ratio for faster speed.
On the other end, a high compression derivative, LZ4_HC, is also provided,
trading CPU time for improved compression ratio.
All versions feature the same decompression speed.

LZ4 is also compatible with [dictionary compression](https://github.com/facebook/zstd#the-case-for-small-data-compression),
both at [API](https://github.com/lz4/lz4/blob/v1.8.3/lib/lz4frame.h#L481) and [CLI](https://github.com/lz4/lz4/blob/v1.8.3/programs/lz4.1.md#operation-modifiers) levels.
It can ingest any input file as dictionary, though only the final 64KB are used.
This capability can be combined with the [Zstandard Dictionary Builder](https://github.com/facebook/zstd/blob/v1.3.5/programs/zstd.1.md#dictionary-builder),
in order to drastically improve compression performance on small files.


LZ4 library is provided as open-source software using BSD 2-Clause license.


|Branch      |Status   |
|------------|---------|
|master      | [![Build Status][travisMasterBadge]][travisLink] [![Build status][AppveyorMasterBadge]][AppveyorLink] [![coverity][coverBadge]][coverlink] |
|dev         | [![Build Status][travisDevBadge]][travisLink]    [![Build status][AppveyorDevBadge]][AppveyorLink]                                         |

[travisMasterBadge]: https://travis-ci.org/lz4/lz4.svg?branch=master "Continuous Integration test suite"
[travisDevBadge]: https://travis-ci.org/lz4/lz4.svg?branch=dev "Continuous Integration test suite"
[travisLink]: https://travis-ci.org/lz4/lz4
[AppveyorMasterBadge]: https://ci.appveyor.com/api/projects/status/github/lz4/lz4?branch=master&svg=true "Windows test suite"
[AppveyorDevBadge]: https://ci.appveyor.com/api/projects/status/github/lz4/lz4?branch=dev&svg=true "Windows test suite"
[AppveyorLink]: https://ci.appveyor.com/project/YannCollet/lz4-1lndh
[coverBadge]: https://scan.coverity.com/projects/4735/badge.svg "Static code analysis of Master branch"
[coverlink]: https://scan.coverity.com/projects/4735

> **Branch Policy:**
> - The "master" branch is considered stable, at all times.
> - The "dev" branch is the one where all contributions must be merged
    before being promoted to master.
>   + If you plan to propose a patch, please commit into the "dev" branch,
      or its own feature branch.
      Direct commit to "master" are not permitted.

Benchmarks
-------------------------

The benchmark uses [lzbench], from @inikep
compiled with GCC v8.2.0 on Linux 64-bits (Ubuntu 4.18.0-17).
The reference system uses a Core i7-9700K CPU @ 4.9GHz (w/ turbo boost).
Benchmark evaluates the compression of reference [Silesia Corpus]
in single-thread mode.

[lzbench]: https://github.com/inikep/lzbench
[Silesia Corpus]: http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia

|  Compressor             | Ratio   | Compression | Decompression |
|  ----------             | -----   | ----------- | ------------- |
|  memcpy                 |  1.000  | 13700 MB/s  |  13700 MB/s   |
|**LZ4 default (v1.9.0)** |**2.101**| **780 MB/s**| **4970 MB/s** |
|  LZO 2.09               |  2.108  |   670 MB/s  |    860 MB/s   |
|  QuickLZ 1.5.0          |  2.238  |   575 MB/s  |    780 MB/s   |
|  Snappy 1.1.4           |  2.091  |   565 MB/s  |   1950 MB/s   |
| [Zstandard] 1.4.0 -1    |  2.883  |   515 MB/s  |   1380 MB/s   |
|  LZF v3.6               |  2.073  |   415 MB/s  |    910 MB/s   |
| [zlib] deflate 1.2.11 -1|  2.730  |   100 MB/s  |    415 MB/s   |
|**LZ4 HC -9 (v1.9.0)**   |**2.721**|    41 MB/s  | **4900 MB/s** |
| [zlib] deflate 1.2.11 -6|  3.099  |    36 MB/s  |    445 MB/s   |

[zlib]: http://www.zlib.net/
[Zstandard]: http://www.zstd.net/

LZ4 is also compatible and optimized for x32 mode,
for which it provides additional speed performance.


Installation
-------------------------

```
make
make install     # this command may require root permissions
```

LZ4's `Makefile` supports standard [Makefile conventions],
including [staged installs], [redirection], or [command redefinition].
It is compatible with parallel builds (`-j#`).

[Makefile conventions]: https://www.gnu.org/prep/standards/html_node/Makefile-Conventions.html
[staged installs]: https://www.gnu.org/prep/standards/html_node/DESTDIR.html
[redirection]: https://www.gnu.org/prep/standards/html_node/Directory-Variables.html
[command redefinition]: https://www.gnu.org/prep/standards/html_node/Utilities-in-Makefiles.html


Documentation
-------------------------

The raw LZ4 block compression format is detailed within [lz4_Block_format].

Arbitrarily long files or data streams are compressed using multiple blocks,
for streaming requirements. These blocks are organized into a frame,
defined into [lz4_Frame_format].
Interoperable versions of LZ4 must also respect the frame format.

[lz4_Block_format]: doc/lz4_Block_format.md
[lz4_Frame_format]: doc/lz4_Frame_format.md


Other source versions
-------------------------

Beyond the C reference source,
many contributors have created versions of lz4 in multiple languages
(Java, C#, Python, Perl, Ruby, etc.).
A list of known source ports is maintained on the [LZ4 Homepage].

[LZ4 Homepage]: http://www.lz4.org