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diff --git a/Build/source/extra/xz/doc/faq.txt b/Build/source/extra/xz/doc/faq.txt deleted file mode 100644 index 333bee09c1c..00000000000 --- a/Build/source/extra/xz/doc/faq.txt +++ /dev/null @@ -1,224 +0,0 @@ - -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 has 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. See <http://7-zip.org/links.html>. - - -Q: Why is liblzma named liblzma if its primary file format is .xz? - Shouldn't it be e.g. libxz? - -A: When the designing of the .xz format began, the idea was to replace - the .lzma format and use the same .lzma suffix. It would have been - quite OK to reuse the suffix when there were very few .lzma files - around. However, the old .lzma format became popular before the - new format was finished. The new format was renamed to .xz but the - name of liblzma wasn't changed. - - -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 of 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. a 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 the 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 than 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. - A streamable version of BCJ2-style filtering is planned. - - -Q: I need to use a script that runs "xz -9". On a system with 256 MiB - of RAM, xz says that it cannot allocate memory. Can I make the - script work without modifying it? - -A: Set a default memory usage limit for compression. You can do it e.g. - in a shell initialization script such as ~/.bashrc or /etc/profile: - - XZ_DEFAULTS=--memlimit-compress=150MiB - export XZ_DEFAULTS - - xz will then scale the compression settings down so that the given - memory usage limit is not reached. This way xz shouldn't run out - of memory. - - Check also that memory-related resource limits are high enough. - On most systems, "ulimit -a" will show the current resource limits. - - -Q: How do I create files that can be decompressed with XZ Embedded? - -A: See the documentation in XZ Embedded. In short, something like - this is a good start: - - xz --check=crc32 --lzma2=preset=6e,dict=64KiB - - Or if a BCJ filter is needed too, e.g. if compressing - a kernel image for PowerPC: - - xz --check=crc32 --powerpc --lzma2=preset=6e,dict=64KiB - - Adjust the dictionary size to get a good compromise between - compression ratio and decompressor memory usage. Note that - in single-call decompression mode of XZ Embedded, a big - dictionary doesn't increase memory usage. - - -Q: Will xz support threaded compression? - -A: It is planned and has been taken into account when designing - the .xz file format. Eventually there will probably be three types - of threading, each method having its own advantages and disadvantages. - - The simplest method is splitting the uncompressed data into blocks - and compressing them in parallel independent from each other. - Since the blocks are compressed independently, they can also be - decompressed independently. Together with the index feature in .xz, - this allows using threads to create .xz files for random-access - reading. This also makes threaded decompression possible, although - it is not clear if threaded decompression will ever be implemented. - - The independent blocks method has a couple of disadvantages too. It - will compress worse than a single-block method. Often the difference - is not too big (maybe 1-2 %) but sometimes it can be too big. Also, - the memory usage of the compressor increases linearly when adding - threads. - - Match finder parallelization is another threading method. It has - been in 7-Zip for ages. It doesn't affect compression ratio or - memory usage significantly. Among the three threading methods, only - this is useful when compressing small files (files that are not - significantly bigger than the dictionary). Unfortunately this method - scales only to about two CPU cores. - - The third method is pigz-style threading (I use that name, because - pigz <http://www.zlib.net/pigz/> uses that method). It doesn't - affect compression ratio significantly and scales to many cores. - The memory usage scales linearly when threads are added. This isn't - significant with pigz, because Deflate uses only a 32 KiB dictionary, - but with LZMA2 the memory usage will increase dramatically just like - with the independent-blocks method. There is also a constant - computational overhead, which may make pigz-method a bit dull on - dual-core compared to the parallel match finder method, but with more - cores the overhead is not a big deal anymore. - - Combining the threading methods will be possible and also useful. - E.g. combining match finder parallelization with pigz-style threading - can cut the memory usage by 50 %. - - It is possible that the single-threaded method will be modified to - create files identical to the pigz-style method. We'll see once - pigz-style threading has been implemented in liblzma. - - -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. You can find it - at <http://tukaani.org/xz/embedded.html>. - |