mirror of https://git.tukaani.org/xz.git
XZ Utils is free general-purpose data compression software with a high compression ratio
https://tukaani.org/xz/
misunderstanding of the code. There's no tiny fix for this problem, so I also cleaned up the code in general. This reduces the speed of the encoder 2-5 % in the fastest compression mode ("lzma -1"). High compression modes should have no noticeable performance difference. This commit breaks things (especially LZMA_SYNC_FLUSH) but I will fix them once the new format and LZMA2 has been roughly implemented. Plain LZMA won't support LZMA_SYNC_FLUSH at all and won't be supported in the new .lzma format. This may change still but this is what it looks like now. Support for known uncompressed size (that is, LZMA or LZMA2 without EOPM) is likely to go away. This means there will be API changes. |
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README
LZMA Utils ---------- Warning This is an early alpha version. Don't trust the files produced by this version of the software - not even if the software can uncompress the files properly! This is because the file format isn't completely frozen yet. So please test a lot, but don't use for anything serious yet. Overview LZMA is a general purporse compression algorithm designed by Igor Pavlov as part of 7-Zip. It provides high compression ratio while keeping the decompression speed fast. LZMA Utils are an attempt to make LZMA compression easy to use on free (as in freedom) operating systems. This is achieved by providing tools and libraries which are similar to use than the equivalents of the most popular existing compression algorithms. LZMA Utils consist of a few relatively separate parts: * liblzma is an encoder/decoder library with support for several filters (algorithm implementations). The primary filter is LZMA. * libzfile enables reading from and writing to gzip, bzip2 and LZMA compressed and uncompressed files with an API similar to the standard ANSI-C file I/O. [ NOTE: libzfile is not implemented yet. ] * lzma command line tool has almost identical syntax than gzip and bzip2. It makes LZMA easy for average users, but also provides advanced options to finetune the compression settings. * A few shell scripts make diffing and grepping LZMA compressed files easy. The scripts were adapted from gzip and bzip2. Supported platforms LZMA Utils are developed on GNU+Linux, but they should work at least on *BSDs and Solaris. They probably work on some other POSIX-like operating systems too. If you use GCC to compile LZMA Utils, you need at least version 3.x.x. GCC version 2.xx.x doesn't support some C99 features used in LZMA Utils source code, thus GCC 2 won't compile LZMA Utils. If you have written patches to make LZMA Utils to work on previously unsupported platform, please send the patches to me! I will consider including them to the official version. It's nice to minimize the need of third-party patching. One exception: Don't request or send patches to change the whole source package to C89. I find C99 substantially nicer to write and maintain. However, the public library headers must be in C89 to avoid frustrating those who maintain programs, which are strictly in C89 or C++. Version numbering Starting from LZMA Utils 5, the version number of LZMA Utils has absolutely nothing to do with the version number of LZMA SDK or 7-Zip. The new version number format of LZMA Utils is X.Y.ZS: - X is the major version. When this is incremented, the library API and ABI break. - Y is the minor version. It is incremented when new features are added without breaking existing API or ABI. Even Y indicates stable release and odd Y indicates unstable (alpha or beta version). - Z is the revision. This has different meaning for stable and unstable releases: * Stable: Z is incremented when bugs get fixed without adding any new features. * Unstable: Z is just a counter. API or ABI of features added in earlier unstable releases having the same X.Y may break. - S indicates stability of the release. It is missing from the stable releases where Y is an even number. When Y is odd, S is either "alpha" or "beta" to make it very clear that such versions are not stable releases. The same X.Y.Z combination is not used for more than one stability level i.e. after X.Y.Zalpha, the next version can be X.Y.(Z+1)beta but not X.Y.Zbeta. configure options If you are not familiar with `configure' scripts, read the file INSTALL first. In most cases, the default --enable/--disable/--with/--without options are what you want. Don't touch them if you are unsure. --disable-encoder Do not compile the encoder component of liblzma. This implies --disable-match-finders. If you need only the decoder, you can decrease the library size dramatically with this option. The default is to build the encoder. --disable-decoder Do not compile the decoder component of liblzma. The default is to build the decoder. --enable-filters= liblzma supports several filters. See liblzma-intro.txt for a little more information about these. The default is to build all the filters. --enable-match-finders= liblzma includes two categories of match finders: hash chains and binary trees. Hash chains (hc3 and hc4) are quite fast but they don't provide the best compression ratio. Binary trees (bt2, bt3 and bt4) give excellent compression ratio, but they are slower and need more memory than hash chains. You need to enable at least one match finder to build the LZMA filter encoder. Usually hash chains are used only in the fast mode, while binary trees are used to when the best compression ratio is wanted. The default is to build all the match finders. --enable-checks= liblzma support multiple integrity checks. CRC32 is mandatory, and cannot be omitted. See liblzma-intro.txt for more information about usage of the integrity checks. --disable-assembler liblzma includes some assembler optimizations. Currently there is only assembler code for CRC32 and CRC64 for 32-bit x86. All the assembler code in liblzma is position-independent code, which is suitable for use in shared libraries and position-independent executables. So far only i386 instructions are used, but the code is optimized for i686 class CPUs. If you are compiling liblzma exclusively for pre-i686 systems, you may want to disable the assembler code. --enable-small Omits precomputed tables. This makes liblzma a few KiB smaller. Startup time increases, because the tables need to be computed first. --enable-debug This enables the assert() macro and possibly some other run-time consistency checks. It slows down things somewhat, so you normally don't want to have this enabled. --enable-werror Makes all compiler warnings an error, that abort the compilation. This may help catching bugs, and should work on most systems. This has no effect on the resulting binaries. Static vs. dynamic linking of the command line tools By default, the command line tools are linked statically against liblzma. There a are a few reasons: - The executable(s) can be in /bin while the shared liblzma can still be in /usr/lib (if the distro uses such file system hierachy). - It's easier to copy the executables to other systems, since they depend only on libc. - It's slightly faster on some architectures like x86. If you don't like this, you can get the command line tools linked against the shared liblzma by specifying --disable-static to configure. This disables building static liblzma completely.