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-
- ============================================================================
- LZO -- a real-time data compression library
- ============================================================================
-
- Author : Markus Franz Xaver Johannes Oberhumer
- <markus@oberhumer.com>
- http://www.oberhumer.com/opensource/lzo/
- Version : 2.07
- Date : 25 Jun 2014
-
-
- Abstract
- --------
- LZO is a portable lossless data compression library written in ANSI C.
- It offers pretty fast compression and very fast decompression.
- Decompression requires no memory.
-
- In addition there are slower compression levels achieving a quite
- competitive compression ratio while still decompressing at
- this very high speed.
-
- The LZO algorithms and implementations are copyrighted OpenSource
- distributed under the GNU General Public License.
-
-
- Introduction
- ------------
- LZO is a data compression library which is suitable for data
- de-/compression in real-time. This means it favours speed
- over compression ratio.
-
- The acronym LZO is standing for Lempel-Ziv-Oberhumer.
-
- LZO is written in ANSI C. Both the source code and the compressed
- data format are designed to be portable across platforms.
-
- LZO implements a number of algorithms with the following features:
-
- - Decompression is simple and *very* fast.
- - Requires no memory for decompression.
- - Compression is pretty fast.
- - Requires 64 KiB of memory for compression.
- - Allows you to dial up extra compression at a speed cost in the
- compressor. The speed of the decompressor is not reduced.
- - Includes compression levels for generating pre-compressed
- data which achieve a quite competitive compression ratio.
- - There is also a compression level which needs only 8 KiB for compression.
- - Algorithm is thread safe.
- - Algorithm is lossless.
-
- LZO supports overlapping compression and in-place decompression.
-
-
- Design criteria
- ---------------
- LZO was designed with speed in mind. Decompressor speed has been
- favoured over compressor speed. Real-time decompression should be
- possible for virtually any application. The implementation of the
- LZO1X decompressor in optimized i386 assembler code runs about at
- the third of the speed of a memcpy() - and even faster for many files.
-
- In fact I first wrote the decompressor of each algorithm thereby
- defining the compressed data format, verified it with manually
- created test data and at last added the compressor.
-
-
- Performance
- -----------
- To keep you interested, here is an overview of the average results
- when compressing the Calgary Corpus test suite with a blocksize
- of 256 KiB, originally done on an ancient Intel Pentium 133.
-
- The naming convention of the various algorithms goes LZOxx-N, where N is
- the compression level. Range 1-9 indicates the fast standard levels using
- 64 KiB memory for compression. Level 99 offers better compression at the
- cost of more memory (256 KiB), and is still reasonably fast.
- Level 999 achieves nearly optimal compression - but it is slow
- and uses much memory, and is mainly intended for generating
- pre-compressed data.
-
- The C version of LZO1X-1 is about 4-5 times faster than the fastest
- zlib compression level, and it also outperforms other algorithms
- like LZRW1-A and LZV in both compression ratio and compression speed
- and decompression speed.
-
- +------------------------------------------------------------------------+
- | Algorithm Length CxB ComLen %Remn Bits Com K/s Dec K/s |
- | --------- ------ --- ------ ----- ---- ------- ------- |
- | |
- | memcpy() 224401 1 224401 100.0 8.00 60956.83 59124.58 |
- | |
- | LZO1-1 224401 1 117362 53.1 4.25 4665.24 13341.98 |
- | LZO1-99 224401 1 101560 46.7 3.73 1373.29 13823.40 |
- | |
- | LZO1A-1 224401 1 115174 51.7 4.14 4937.83 14410.35 |
- | LZO1A-99 224401 1 99958 45.5 3.64 1362.72 14734.17 |
- | |
- | LZO1B-1 224401 1 109590 49.6 3.97 4565.53 15438.34 |
- | LZO1B-2 224401 1 106235 48.4 3.88 4297.33 15492.79 |
- | LZO1B-3 224401 1 104395 47.8 3.83 4018.21 15373.52 |
- | LZO1B-4 224401 1 104828 47.4 3.79 3024.48 15100.11 |
- | LZO1B-5 224401 1 102724 46.7 3.73 2827.82 15427.62 |
- | LZO1B-6 224401 1 101210 46.0 3.68 2615.96 15325.68 |
- | LZO1B-7 224401 1 101388 46.0 3.68 2430.89 15361.47 |
- | LZO1B-8 224401 1 99453 45.2 3.62 2183.87 15402.77 |
- | LZO1B-9 224401 1 99118 45.0 3.60 1677.06 15069.60 |
- | LZO1B-99 224401 1 95399 43.6 3.48 1286.87 15656.11 |
- | LZO1B-999 224401 1 83934 39.1 3.13 232.40 16445.05 |
- | |
- | LZO1C-1 224401 1 111735 50.4 4.03 4883.08 15570.91 |
- | LZO1C-2 224401 1 108652 49.3 3.94 4424.24 15733.14 |
- | LZO1C-3 224401 1 106810 48.7 3.89 4127.65 15645.69 |
- | LZO1C-4 224401 1 105717 47.7 3.82 3007.92 15346.44 |
- | LZO1C-5 224401 1 103605 47.0 3.76 2829.15 15153.88 |
- | LZO1C-6 224401 1 102585 46.5 3.72 2631.37 15257.58 |
- | LZO1C-7 224401 1 101937 46.2 3.70 2378.57 15492.49 |
- | LZO1C-8 224401 1 100779 45.6 3.65 2171.93 15386.07 |
- | LZO1C-9 224401 1 100255 45.4 3.63 1691.44 15194.68 |
- | LZO1C-99 224401 1 97252 44.1 3.53 1462.88 15341.37 |
- | LZO1C-999 224401 1 87740 40.2 3.21 306.44 16411.94 |
- | |
- | LZO1F-1 224401 1 113412 50.8 4.07 4755.97 16074.12 |
- | LZO1F-999 224401 1 89599 40.3 3.23 280.68 16553.90 |
- | |
- | LZO1X-1(11) 224401 1 118810 52.6 4.21 4544.42 15879.04 |
- | LZO1X-1(12) 224401 1 113675 50.6 4.05 4411.15 15721.59 |
- | LZO1X-1 224401 1 109323 49.4 3.95 4991.76 15584.89 |
- | LZO1X-1(15) 224401 1 108500 49.1 3.93 5077.50 15744.56 |
- | LZO1X-999 224401 1 82854 38.0 3.04 135.77 16548.48 |
- | |
- | LZO1Y-1 224401 1 110820 49.8 3.98 4952.52 15638.82 |
- | LZO1Y-999 224401 1 83614 38.2 3.05 135.07 16385.40 |
- | |
- | LZO1Z-999 224401 1 83034 38.0 3.04 133.31 10553.74 |
- | |
- | LZO2A-999 224401 1 87880 40.0 3.20 301.21 8115.75 |
- +------------------------------------------------------------------------+
-
- Notes:
- - CxB is the number of blocks
- - K/s is the speed measured in 1000 uncompressed bytes per second
- - the assembler decompressors are even faster
-
-
- Short documentation
- -------------------
- LZO is a block compression algorithm - it compresses and decompresses
- a block 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. LZO takes care about long matches
- and long literal runs so that it produces good results on highly
- redundant data and deals acceptably with non-compressible data.
-
- When dealing with incompressible data, LZO expands the input
- block by a maximum of 64 bytes per 1024 bytes input.
-
- I have verified LZO using such tools as valgrind and other memory checkers.
- And in addition to compressing gigabytes of files when tuning some parameters
- I have also consulted various 'lint' programs to spot potential portability
- problems. LZO is free of any known bugs.
-
-
- The algorithms
- --------------
- There are too many algorithms implemented. But I want to support
- unlimited backward compatibility, so I will not reduce the LZO
- distribution in the future.
-
- As the many object files are mostly independent of each other, the
- size overhead for an executable statically linked with the LZO library
- is usually pretty low (just a few KiB) because the linker will only add
- the modules that you are actually using.
-
- I first published LZO1 and LZO1A in the Internet newsgroups
- comp.compression and comp.compression.research in March 1996.
- They are mainly included for compatibility reasons. The LZO2A
- decompressor is too slow, and there is no fast compressor anyway.
-
- My experiments have shown that LZO1B is good with a large blocksize
- or with very redundant data, LZO1F is good with a small blocksize or
- with binary data and that LZO1X is often the best choice of all.
- LZO1Y and LZO1Z are almost identical to LZO1X - they can achieve a
- better compression ratio on some files.
- Beware, your mileage may vary.
-
-
- Usage of the library
- --------------------
- Despite of its size, the basic usage of LZO is really very simple.
-
- Let's assume you want to compress some data with LZO1X-1:
- A) compression
- * include <lzo/lzo1x.h>
- call lzo_init()
- compress your data with lzo1x_1_compress()
- * link your application with the LZO library
- B) decompression
- * include <lzo/lzo1x.h>
- call lzo_init()
- decompress your data with lzo1x_decompress()
- * link your application with the LZO library
-
- The program examples/simple.c shows a fully working example.
- See also LZO.FAQ for more information.
-
-
- Building LZO
- ------------
- As LZO uses Autoconf+Automake+Libtool the building process under
- UNIX systems should be very unproblematic. Shared libraries are
- supported on many architectures as well.
- For detailed instructions see the file INSTALL.
-
- Please note that due to the design of the ELF executable format
- the performance of a shared library on i386 systems (e.g. Linux)
- is a little bit slower, so you may want to link your applications
- with the static version (liblzo2.a) anyway.
-
- For building under DOS, Win16, Win32, OS/2 and other systems
- take a look at the file B/00readme.txt.
-
- In case of troubles (like decompression data errors) try recompiling
- everything without optimizations - LZO may break the optimizer
- of your compiler. See the file BUGS.
-
- LZO is written in ANSI C. In particular this means:
- - your compiler must understand prototypes
- - your compiler must understand prototypes in function pointers
- - your compiler must correctly promote integrals ("value-preserving")
- - your preprocessor must implement #elif, #error and stringizing
- - you must have a conforming and correct <limits.h> header
- - you must have <stddef.h>, <string.h> and other ANSI C headers
- - you should have size_t and ptrdiff_t
-
-
- Portability
- -----------
- I have built and tested LZO successfully on a variety of platforms
- including DOS (16 + 32 bit), Windows 3.x (16-bit), Win32, Win64,
- Linux, *BSD, HP-UX and many more.
-
- LZO is also reported to work under AIX, ConvexOS, IRIX, MacOS, PalmOS (Pilot),
- PSX (Sony Playstation), Solaris, SunOS, TOS (Atari ST) and VxWorks.
- Furthermore it is said that its performance on a Cray is superior
- to all other machines...
-
- And I think it would be much fun to translate the decompressors
- to Z-80 or 6502 assembly.
-
-
- The future
- ----------
- Here is what I'm planning for the next months. No promises, though...
-
- - interfaces to .NET and Mono
- - interfaces to Perl, Java, Python, Delphi, Visual Basic, ...
- - improve documentation and API reference
-
-
- Some comments about the source code
- -----------------------------------
- Be warned: the main source code in the 'src' directory is a
- real pain to understand as I've experimented with hundreds of slightly
- different versions. It contains many #if and some gotos, and
- is *completely optimized for speed* and not for readability.
- Code sharing of the different algorithms is implemented by stressing
- the preprocessor - this can be really confusing. Lots of marcos and
- assertions don't make things better.
-
- Nevertheless LZO compiles very quietly on a variety of
- compilers with the highest warning levels turned on, even
- in C++ mode.
-
-
- Copyright
- ---------
- LZO is Copyright (C) 1996-2014 Markus Franz Xaver Oberhumer
- All Rights Reserved.
-
- LZO is distributed under the terms of the GNU General Public License (GPL).
- See the file COPYING.
-
- Special licenses for commercial and other applications which
- are not willing to accept the GNU General Public License
- are available by contacting the author.
-
-
-