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+
+LZMA Utils FAQ
+--------------
+
+    Copyright (C) 2007 Lasse Collin
+
+    Copying and distribution of this file, with or without modification,
+    are permitted in any medium without royalty provided the copyright
+    notice and this notice are preserved.
+
+
+Q:  What are LZMA, LZMA Utils, lzma, .lzma, liblzma, LZMA SDK, LZMA_Alone,
+    7-Zip and p7zip?
+
+A:  LZMA stands for Lempel-Ziv-Markov chain-Algorithm. LZMA is the name
+    of the compression algorithm designed by Igor Pavlov. He is the author
+    of 7-Zip, which is a great LGPL'd compression tool for Microsoft
+    Windows operating systems. In addition to 7-Zip itself, also LZMA SDK
+    is available on the website of 7-Zip. LZMA SDK contains LZMA
+    implementations in C++, Java and C#. The C++ version is the original
+    implementation which is used also in 7-Zip itself.
+
+    Excluding the unrar plugin, 7-Zip is free software (free as in
+    freedom). Thanks to this, it was possible to port it to POSIX
+    platforms. The port was done and is maintained by myspace (TODO:
+    myspace's real name?). p7zip is a port of 7-Zip's command line version;
+    p7zip doesn't include the 7-Zip's GUI.
+
+    In POSIX world, users are used to gzip and bzip2 command line tools.
+    Developers know APIs of zlib and libbzip2. LZMA Utils try to ease
+    adoption of LZMA on free operating systems by providing a compression
+    library and a set of command line tools. The library is called liblzma.
+    It provides a zlib-like API making it easy to adapt LZMA compression in
+    existing applications. The main command line tool is known as lzma,
+    whose command line syntax is very similar to that of gzip and bzip2.
+
+    The original command line tool from LZMA SDK (lzma.exe) was found from
+    a directory called LZMA_Alone in the LZMA SDK. It used a simple header
+    format in .lzma files. This format was also used by LZMA Utils up to
+    and including 4.32.x. In LZMA Utils documentation, LZMA_Alone refers
+    to both the file format and the command line tool from LZMA SDK.
+
+    Because of various limitations of the LZMA_Alone file format, a new
+    file format was developed. Extending some existing format such as .gz
+    used by gzip was considered, but these formats were found to be too
+    limited. The filename suffix for the new .lzma format is `.lzma'. The
+    same suffix is also used for files in the LZMA_Alone format. To make
+    the transition to the new format as transparent as possible, LZMA Utils
+    support both the new and old formats transparently.
+
+    7-Zip and LZMA SDK: <http://7-zip.org/>
+    p7zip: <http://p7zip.sourceforge.net/>
+    LZMA Utils: <http://tukaani.org/lzma/>
+
+
+Q:  What LZMA implementations there are available?
+
+A:  LZMA SDK contains implementations in C++, Java and C#. The C++ version
+    is the original implementation which is part of 7-Zip. LZMA SDK
+    contains also a small LZMA decoder in C.
+
+    A port of LZMA SDK to Pascal was made by Alan Birtles
+    <http://www.birtles.org.uk/programming/>. It should work with
+    multiple Pascal programming language implementations.
+
+    LZMA Utils includes liblzma, which is directly based on LZMA SDK.
+    liblzma is written in C (C99, not C89). In contrast to C++ callback
+    API used by LZMA SDK, liblzma uses zlib-like stateful C API. I do not
+    want to comment whether both/former/latter/neither API(s) are good or
+    bad. The only reason to implement a zlib-like API was, that many
+    developers are already familiar with zlib, and very many applications
+    already use zlib. Having a similar API makes it easier to include LZMA
+    support in existing applications.
+
+    See also <http://en.wikipedia.org/wiki/LZMA#External_links>.
+
+
+Q:  Which file formats are supported by LZMA Utils?
+
+A:  Even when the raw LZMA stream is always the same, it can be wrapped
+    in different container formats. The preferred format is the new .lzma
+    format. It has magic bytes (the first six bytes: 0xFF 'L' 'Z' 'M'
+    'A' 0x00). The format supports chaining up to seven filters filters,
+    splitting data to multiple blocks for easier multi-threading and rough
+    random-access reading. The file integrity is verified using CRC32,
+    CRC64, or SHA256, and by verifying the uncompressed size of the file.
+
+    LZMA SDK includes a tool called LZMA_Alone. It supports uses a
+    primitive header which includes only the mandatory stream information
+    required by the LZMA decoder. This format can be both read and
+    written by liblzma and the command line tool (use --format=alone to
+    create such files).
+
+    .7z is the native archive format used by 7-Zip. This format is not
+    supported by liblzma, and probably will never be supported. You
+    should use e.g. p7zip to extract .7z files.
+
+    It is possible to implement custom file formats by using raw filter
+    mode in liblzma. In this mode the application needs to store the filter
+    properties and provide them to liblzma before starting to uncompress
+    the data.
+
+
+Q:  How can I identify files containing LZMA compressed data?
+
+A:  The preferred filename suffix for .lzma files is `.lzma'. `.tar.lzma'
+    may be abbreviated to `.tlz'. The same suffixes are used for files in
+    LZMA_Alone format. In practice this should be no problem since tools
+    included in LZMA Utils support both formats transparently.
+
+    Checking the magic bytes is easy way to detect files in the new .lzma
+    format (the first six bytes: 0xFF 'L' 'Z' 'M' 'A' 0x00). The "file"
+    command version FIXME contains magic strings for this format.
+
+    The old LZMA_Alone format has no magic bytes. Its header cannot contain
+    arbitrary bytes, thus it is possible to make a guess. Unfortunately the
+    guessing is usually too hard to be reliable, so don't try it unless you
+    are desperate.
+
+
+Q:  Does the lzma command line tool support sparse files?
+
+A:  Sparse files can (of course) be compressed like normal files, but
+    uncompression will not restore sparseness of the file. Use an archiver
+    tool to take care of sparseness before compressing the data with lzma.
+
+    The reason for this is that archiver tools handle files, while
+    compression tools handle streams or buffers. Being a sparse file is
+    a property of the file on the disk, not a property of the stream or
+    buffer.
+
+
+Q:  Can I recover parts of a broken LZMA file (e.g. corrupted CD-R)?
+
+A:  With LZMA_Alone and single-block .lzma files, you can uncompress the
+    file until you hit the first broken byte. The data after the broken
+    position is lost. LZMA relies on the uncompression history, and if
+    bytes are missing in the middle of the file, it is impossible to
+    reliably continue after the broken section.
+
+    With multi-block .lzma files it may be possible to locale the next
+    block in the file and continue decoding there. A limited recovery
+    tool for this kind of situations is planned.
+
+
+Q:  Is LZMA patented?
+
+A:  No, the authors are not aware of any patents that could affect LZMA.
+    However, due to nature of software patents, the authors cannot
+    guarantee, that LZMA isn't affected by any third party patent.
+
+
+Q:  Where can I find documentation about how LZMA works as an algorithm?
+
+A:  Read the source code, Luke. There is no documentation about LZMA
+    internals. It is possible that Igor Pavlov is the only person on
+    the Earth that completely knows and understands the algorithm.
+
+    You could begin by downloading LZMA SDK, and start reading from
+    the LZMA decoder to get some idea about the bitstream format.
+    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:  What are filters?
+
+A:  In context of .lzma files, a filter means an implementation of a
+    compression algorithm. The primary filter is LZMA, which is why
+    the names of the tools contain the letters LZMA.
+
+    liblzma and the new .lzma format support also other filters than LZMA.
+    There are different types of filters, which are suitable for different
+    types of data. Thus, to select the optimal filter and settings, the
+    type of the input data being compressed needs to be known.
+
+    Some filters are most useful when combined with another filter like
+    LZMA. These filters increase redundancy in the data, without changing
+    the size of the data, by taking advantage of properties specific to
+    the data being compressed.
+
+    So far, all the filters are always reversible. That is, no matter what
+    data you pass to a filter encoder, it can be always defiltered back to
+    the original form. Because of this, it is safe to compress for example
+    a software package that contains other file types than executables
+    using a filter specific to the architechture of the package being
+    compressed.
+
+    The old LZMA_Alone format supports only the LZMA filter.
+
+
+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:  Can I use LZMA in proprietary, non-free applications?
+
+A:  liblzma is under the GNU LGPL version 2.1 or (at your opinion) any
+    later version. To summarise (*NOTE* This summary is not legally
+    binding, that is, it doesn't give you any extra permissions compared
+    to the LGPL. Read the GNU LGPL carefully for the exact license
+    conditions.):
+      * All the changes made into the library itself must be published
+        under the same license.
+      * End users must be able to replace the used liblzma. Easiest way
+        to assure this is to link dynamically against liblzma so users
+        can replace the shared library file if they want.
+      * You must make it clear to your users, that your application uses
+        liblzma, and that liblzma is free software under the GNU LGPL.
+        A copy of GNU LGPL must be included.
+
+    LZMA SDK contains a special exception which allows linking *unmodified*
+    code statically with a non-free application. This exception does *not*
+    apply to liblzma.
+
+    As an alternative, you can support the development of LZMA and 7-Zip
+    by buying a proprietary license from Igor Pavlov. See homepage of
+    LZMA SDK <http://7-zip.org/sdk.html> for more information. Note that
+    having a proprietary license from Igor Pavlov doesn't allow you to use
+    liblzma in a way that contradicts with the GNU LGPL, because liblzma
+    contains code that is not copyrighted by Igor Pavlov. Please contact
+    both Lasse Collin and Igor Pavlov if the license conditions of liblzma
+    are not suitable for you.
+
+
+Q:  I would like to help. What can I do?
+
+A:  See the TODO file. Please contact Lasse Collin before starting to do
+    anything, because it is possible that someone else is already working
+    on the same thing.
+
+
+Q:  How can I contact the authors?
+
+A:  Lasse Collin is the maintainer of LZMA Utils. You can contact him
+    either via IRC (Larhzu on #tukaani at Freenode or IRCnet). Email
+    should work too, <lasse.collin@tukaani.org>.
+
+    Igor Pavlov is the father of LZMA. He is the author of 7-Zip
+    and LZMA SDK. <http://7-zip.org/>
+
+    NOTE: Please don't bother Igor Pavlov with questions specific
+    to LZMA Utils.
+