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diff --git a/doc/LZO.TXT b/doc/LZO.TXT new file mode 100644 index 0000000..7426ab2 --- /dev/null +++ b/doc/LZO.TXT @@ -0,0 +1,292 @@ + + ============================================================================ + LZO -- a real-time data compression library + ============================================================================ + + Author : Markus Franz Xaver Johannes Oberhumer + <markus@oberhumer.com> + http://www.oberhumer.com/opensource/lzo/ + Version : 2.06 + Date : 12 Aug 2011 + + + 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, 1997, 1998, 1999, 2000, 2001, 2002, + 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 + Markus Franz Xaver Oberhumer <markus@oberhumer.com>. + + 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. + + + |