195 lines
8.1 KiB
Plaintext
195 lines
8.1 KiB
Plaintext
|
|
XZ Utils
|
|
========
|
|
|
|
Important
|
|
|
|
This is a beta version. The .xz file format is now stable though,
|
|
which means that files created with the beta version will be
|
|
uncompressible with all future XZ Utils versions too (assuming
|
|
that there are no catastrophical bugs).
|
|
|
|
liblzma API is pretty stable now, although minor tweaks may still
|
|
be done if really needed. The ABI is not stable yet. The major
|
|
soname will be bumped right before the first stable release.
|
|
Probably it will be bumped to something like .so.5.0.0 because
|
|
some distributions using the alpha versions already had to use
|
|
other versions than .so.0.0.0.
|
|
|
|
Excluding the Doxygen style docs in libilzma API headers, the
|
|
documentation in this package (including the rest of this
|
|
README) is not very up to date, and may contain incorrect or
|
|
misleading information.
|
|
|
|
|
|
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.
|
|
|
|
XZ 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.
|
|
|
|
XZ 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 (or whatever the name will be) 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. ]
|
|
* xz 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
|
|
|
|
XZ 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 XZ Utils, you need at least version
|
|
3.x.x. GCC version 2.xx.x doesn't support some C99 features used
|
|
in XZ Utils source code, thus GCC 2 won't compile XZ Utils.
|
|
|
|
If you have written patches to make XZ 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
|
|
|
|
The version number of XZ Utils has absolutely nothing to do with
|
|
the version number of LZMA SDK or 7-Zip. The new version number
|
|
format of XZ 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.
|
|
|