Add an unpatched version of xz, XZ Utils, to /trunk/deps/third_party

xz/doc/faq.txt

+
+XZ Utils FAQ
+============
+
+Q:  What do the letters XZ mean?
+
+A:  Nothing. They are just two letters, which come from the file format
+    suffix .xz. The .xz suffix was selected, because it seemed to be
+    pretty much unused. It is no deeper meaning.
+
+
+Q:  What are LZMA and LZMA2?
+
+A:  LZMA stands for Lempel-Ziv-Markov chain-Algorithm. It is the name
+    of the compression algorithm designed by Igor Pavlov for 7-Zip.
+    LZMA is based on LZ77 and range encoding.
+
+    LZMA2 is an updated version of the original LZMA to fix a couple of
+    practical issues. In context of XZ Utils, LZMA is called LZMA1 to
+    emphasize that LZMA is not the same thing as LZMA2. LZMA2 is the
+    primary compression algorithm in the .xz file format.
+
+
+Q:  There are many LZMA related projects. How does XZ Utils relate to them?
+
+A:  7-Zip and LZMA SDK are the original projects. LZMA SDK is roughly
+    a subset of the 7-Zip source tree.
+
+    p7zip is 7-Zip's command line tools ported to POSIX-like systems.
+
+    LZMA Utils provide a gzip-like lzma tool for POSIX-like systems.
+    LZMA Utils are based on LZMA SDK. XZ Utils are the successor to
+    LZMA Utils.
+
+    There are several other projects using LZMA. Most are more or less
+    based on LZMA SDK.
+
+
+Q:  Do XZ Utils support the .7z format?
+
+A:  No. Use 7-Zip (Windows) or p7zip (POSIX-like systems) to handle .7z
+    files.
+
+
+Q:  I have many .tar.7z files. Can I convert them to .tar.xz without
+    spending hours recompressing the data?
+
+A:  In the "extra" directory, there is a script named 7z2lzma.bash which
+    is able to convert some .7z files to the .lzma format (not .xz). It
+    needs the 7za (or 7z) command from p7zip. The script may silently
+    produce corrupt output if certain assumptions are not met, so
+    decompress the resulting .lzma file and compare it against the
+    original before deleting the original file!
+
+
+Q:  I have many .lzma files. Can I quickly convert them to the .xz format?
+
+A:  For now, no. Since XZ Utils supports the .lzma format, it's usually
+    not too bad to keep the old files in the old format. If you want to
+    do the conversion anyway, you need to decompress the .lzma files and
+    then recompress to the .xz format.
+
+    Technically, there is a way to make the conversion relatively fast
+    (roughly twice the time that normal decompression takes). Writing
+    such a tool would take quite a bit time though, and would probably
+    be useful to only a few people. If you really want such a conversion
+    tool, contact Lasse Collin and offer some money.
+
+
+Q:  I have installed xz, but my tar doesn't recognize .tar.xz files.
+    How can I extract .tar.xz files?
+
+A:  xz -dc foo.tar.xz | tar xf -
+
+
+Q:  Can I recover parts of a broken .xz file (e.g. corrupted CD-R)?
+
+A:  It may be possible if the file consists of multiple blocks, which
+    typically is not the case if the file was created in single-threaded
+    mode. There is no recovery program yet.
+
+
+Q:  Is (some part of) XZ Utils patented?
+
+A:  Lasse Collin is not aware of any patents that could affect XZ Utils.
+    However, due to nature of software patents, it's not possible to
+    guarantee that XZ Utils isn't affected by any third party patent(s).
+
+
+Q:  Where can I find documentation about the file format and algorithms?
+
+A:  The .xz format is documented in xz-file-format.txt. It is a container
+    format only, and doesn't include descriptions of any non-trivial
+    filters.
+
+    Documenting LZMA and LZMA2 is planned, but for now, there is no other
+    documentation that the source code. Before you begin, you should know
+    the basics of LZ77 and range coding algorithms. LZMA is based on LZ77,
+    but LZMA is *a lot* more complex. Range coding is used to compress
+    the final bitstream like Huffman coding is used in Deflate.
+
+
+Q:  I cannot find BCJ and BCJ2 filters. Don't they exist in liblzma?
+
+A:  BCJ filter is called "x86" in liblzma. BCJ2 is not included,
+    because it requires using more than one encoded output stream.
+
+
+Q:  How do I build a program that needs liblzmadec (lzmadec.h)?
+
+A:  liblzmadec is part of LZMA Utils. XZ Utils has liblzma, but no
+    liblzmadec. The code using liblzmadec should be ported to use
+    liblzma instead. If you cannot or don't want to do that, download
+    LZMA Utils from <http://tukaani.org/lzma/>.
+
+
+Q:  The default build of liblzma is too big. How can I make it smaller?
+
+A:  Give --enable-small to the configure script. Use also appropriate
+    --enable or --disable options to include only those filter encoders
+    and decoders and integrity checks that you actually need. Use
+    CFLAGS=-Os (with GCC) or equivalent to tell your compiler to optimize
+    for size. See INSTALL for information about configure options.
+
+    If the result is still too big, take a look at XZ Embedded. It is
+    a separate project, which provides a limited but significantly
+    smaller XZ decoder implementation than XZ Utils.
+