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XZ Embedded
===========
XZ Embedded is a relatively small, limited implementation of the .xz
file format. Currently only decoding is implemented.
XZ Embedded was written for use in the Linux kernel, but the code can
be easily used in other environments too, including regular userspace
applications.
This README contains information that is useful only when the copy
of XZ Embedded isn't part of the Linux kernel tree. You should also
read linux/Documentation/xz.txt even if you aren't using XZ Embedded
as part of Linux; information in that file is not repeated in this
README.
Compiling the Linux kernel module
cd linux/lib/xz
make -C /path/to/kernel/source \
CONFIG_XZ_DEC=m KCPPFLAGS=-I"$(pwd)/../../include" M="$(pwd)"
The xz_dec module depends on crc32 module, so make sure that you have
it enabled (CONFIG_CRC32).
Compiler requirements
XZ Embedded should compile as either GNU-C89 (used in the Linux
kernel) or with any C99 compiler. Getting the code to compile with
non-GNU C89 compiler or a C++ compiler should be quite easy as
long as there is a data type for unsigned 64-bit integer (or the
code is modified not to support large files, which needs some more
care than just using 32-bit integer instead of 64-bit).
If you use GCC, try to use a recent version. For example, on x86,
xz_dec_lzma2.c compiled with GCC 3.3.6 is 15-25 % slower than when
compiled with GCC 4.3.3.
Embedding into userspace applications
To embed the XZ decoder, copy the following files into a single
directory in your source code tree:
linux/include/linux/xz.h
linux/lib/xz/xz_crc32.c
linux/lib/xz/xz_dec_lzma2.c
linux/lib/xz/xz_dec_stream.c
linux/lib/xz/xz_lzma2.h
linux/lib/xz/xz_private.h
linux/lib/xz/xz_stream.h
Alternatively, xz.h may be placed into a different directory but then
that directory must be in the compiler include path when compiling
the .c files.
Your code should use only the functions declared in xz.h. The rest of
the .h files are meant only for internal use in XZ Embedded.
If you are including XZ Embedded into a shared library, you very
probably should rename the xz_* functions to prevent symbol
conflicts in case your library is linked against some other library
or application that also has XZ Embedded in it (which may even be
a different version of XZ Embedded). TODO: Provide an easy way
to do this.
NOTE: Please don't create a shared library of XZ Embedded itself
unless it is fine to rebuild everything depending on that shared
library everytime you upgrade to a newer version of XZ Embedded.
There are no API or ABI stability guarantees between different
versions of XZ Embedded.
Specifying the calling convention
XZ_FUNC macro was included to support declaring functions with __init
in Linux. Outside Linux, it can be used to specify the calling
convention on systems that support multiple calling conventions.
For example, on Windows, you may make all functions to use the stdcall
calling convention by defining XZ_FUNC=__stdcall when building and
using the functions from XZ Embedded.
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