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Lzlib is a data compression library providing in-memory LZMA compression and decompression functions, including integrity checking of the decompressed data. The compressed data format used by the library is the lzip format. Lzlib is written in C.

The lzip file format is designed for data sharing and long-term archiving, taking into account both data integrity and decoder availability:

A nice feature of the lzip format is that a corrupt byte is easier to repair the nearer it is from the beginning of the file. Therefore, with the help of lziprecover, losing an entire archive just because of a corrupt byte near the beginning is a thing of the past.

The functions and variables forming the interface of the compression library are declared in the file 'lzlib.h'. Usage examples of the library are given in the files 'main.c' and 'bbexample.c' from the source distribution.

Compression/decompression is done by repeatedly calling a couple of read/write functions until all the data have been processed by the library. This interface is safer and less error prone than the traditional zlib interface.

Compression/decompression is done when the read function is called. This means the value returned by the position functions will not be updated until a read call, even if a lot of data is written. If you want the data to be compressed in advance, just call the read function with a size equal to 0.

If all the data to be compressed are written in advance, lzlib will automatically adjust the header of the compressed data to use the smallest possible dictionary size. This feature reduces the amount of memory needed for decompression and allows minilzip to produce identical compressed output as lzip.

Lzlib will correctly decompress a data stream which is the concatenation of two or more compressed data streams. The result is the concatenation of the corresponding decompressed data streams. Integrity testing of concatenated compressed data streams is also supported.

All the library functions are thread safe. The library does not install any signal handler. The decoder checks the consistency of the compressed data, so the library should never crash even in case of corrupted input.

Learn more about lzip in the Lzip Home Page.


The manual is available in the info system of the GNU Operating System. Use info to access the top level info page. Use info lzlib to access the lzlib section directly.

An online manual for lzlib can be found here.


The latest released version of lzlib can be found here. You may also subscribe to lzip-bug and receive an email every time a new version is released.

How to get help

For general discussion of bugs in lzlib the mailing list lzip-bug@nongnu.org is the most appropriate forum. Please send messages as plain text. Please do not send messages encoded as HTML nor encoded as base64 MIME nor included as multiple formats. Please include a descriptive subject line. If all of the subject are "bug in lzlib" it is impossible to differentiate them.

An archive of the bug report mailing list is available at http://lists.gnu.org/mailman/listinfo/lzip-bug.

How to help

To contact the author, either to report a bug or to contribute fixes or improvements, send mail to lzip-bug@nongnu.org. Please send messages as plain text. If posting patches they should be in unified diff format against the latest version. They should include a text description.

See also the lzip project page at Savannah.


Lzlib is free software distributed under a 2-clause BSD license.

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Copyright © 2017 Antonio Diaz Diaz
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Updated: 2017-07-17