152 lines
6.1 KiB
Plaintext
152 lines
6.1 KiB
Plaintext
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LZMA Utils
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----------
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Warning
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This is an early alpha version. Don't trust the files produced by
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this version of the software - not even if the software can
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uncompress the files properly! This is because the file format
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isn't completely frozen yet.
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So please test a lot, but don't use for anything serious yet.
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Overview
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LZMA is a general purporse compression algorithm designed by
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Igor Pavlov as part of 7-Zip. It provides high compression ratio
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while keeping the decompression speed fast.
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LZMA Utils are an attempt to make LZMA compression easy to use
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on free (as in freedom) operating systems. This is achieved by
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providing tools and libraries which are similar to use than the
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equivalents of the most popular existing compression algorithms.
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LZMA Utils consist of a few relatively separate parts:
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* liblzma is an encoder/decoder library with support for several
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filters (algorithm implementations). The primary filter is LZMA.
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* libzfile enables reading from and writing to gzip, bzip2 and
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LZMA compressed and uncompressed files with an API similar to
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the standard ANSI-C file I/O.
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[ NOTE: libzfile is not implemented yet. ]
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* lzma command line tool has almost identical syntax than gzip
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and bzip2. It makes LZMA easy for average users, but also
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provides advanced options to finetune the compression settings.
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* A few shell scripts make diffing and grepping LZMA compressed
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files easy. The scripts were adapted from gzip and bzip2.
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Supported platforms
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LZMA Utils are developed on GNU+Linux, but they should work at
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least on *BSDs and Solaris. They probably work on some other
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POSIX-like operating systems too.
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If you use GCC to compile LZMA Utils, you need at least version
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3.x.x. GCC version 2.xx.x doesn't support some C99 features used
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in LZMA Utils source code, thus GCC 2 won't compile LZMA Utils.
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If you have written patches to make LZMA Utils to work on previously
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unsupported platform, please send the patches to me! I will consider
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including them to the official version. It's nice to minimize the
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need of third-party patching.
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One exception: Don't request or send patches to change the whole
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source package to C89. I find C99 substantially nicer to write and
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maintain. However, the public library headers must be in C89 to
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avoid frustrating those who maintain programs, which are strictly
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in C89 or C++.
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configure options
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If you are not familiar with `configure' scripts, read the file
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INSTALL first.
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In most cases, the default --enable/--disable/--with/--without options
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are what you want. Don't touch them if you are unsure.
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--disable-encoder
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Do not compile the encoder component of liblzma. This
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implies --disable-match-finders. If you need only
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the decoder, you can decrease the library size
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dramatically with this option.
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The default is to build the encoder.
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--disable-decoder
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Do not compile the decoder component of liblzma.
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The default is to build the decoder.
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--enable-filters=
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liblzma supports several filters. See liblzma-intro.txt
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for a little more information about these.
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The default is to build all the filters.
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--enable-match-finders=
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liblzma includes two categories of match finders:
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hash chains and binary trees. Hash chains (hc3 and hc4)
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are quite fast but they don't provide the best compression
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ratio. Binary trees (bt2, bt3 and bt4) give excellent
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compression ratio, but they are slower and need more
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memory than hash chains.
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You need to enable at least one match finder to build the
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LZMA filter encoder. Usually hash chains are used only in
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the fast mode, while binary trees are used to when the best
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compression ratio is wanted.
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The default is to build all the match finders.
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--enable-checks=
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liblzma support multiple integrity checks. CRC32 is
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mandatory, and cannot be omitted. See liblzma-intro.txt
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for more information about usage of the integrity checks.
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--disable-assembler
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liblzma includes some assembler optimizations. Currently
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there is only assembler code for CRC32 and CRC64 for
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32-bit x86.
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All the assembler code in liblzma is position-independent
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code, which is suitable for use in shared libraries and
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position-independent executables.
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--enable-small
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Omits precomputed tables. This makes liblzma a few KiB
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smaller. Startup time increases, because the tables need
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to be computed first.
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--enable-debug
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This enables the assert() macro and possibly some other
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run-time consistency checks. It slows down things somewhat,
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so you normally don't want to have this enabled.
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--enable-werror
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Makes all compiler warnings an error, that abort the
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compilation. This may help catching bugs, and should work
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on most systems. This has no effect on the resulting
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binaries.
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Static vs. dynamic linking of the command line tools
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By default, the command line tools are linked statically against
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liblzma. There a are a few reasons:
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- The executable(s) can be in /bin while the shared liblzma can still
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be in /usr/lib (if the distro uses such file system hierachy).
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- It's easier to copy the executables to other systems, since they
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depend only on libc.
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- It's slightly faster on some architectures like x86.
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If you don't like this, you can get the command line tools linked
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against the shared liblzma by specifying --disable-static to configure.
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This disables building static liblzma completely.
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