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diff --git a/Build/source/extra/xz-4.999.9beta-124-gb637/doc/faq.txt b/Build/source/extra/xz-4.999.9beta-124-gb637/doc/faq.txt new file mode 100644 index 00000000000..8e87457a594 --- /dev/null +++ b/Build/source/extra/xz-4.999.9beta-124-gb637/doc/faq.txt @@ -0,0 +1,128 @@ + +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. + |