src/cmd/bzip2/README - plan9 - Git at Google


 This is the README for bzip2, a block-sorting file compressor, version
 1.0.  This version is fully compatible with the previous public
 releases, bzip2-0.1pl2, bzip2-0.9.0 and bzip2-0.9.5.

 bzip2-1.0 is distributed under a BSD-style license.  For details,
 see the file LICENSE.

 Complete documentation is available in Postscript form (manual.ps) or
 html (manual_toc.html).  A plain-text version of the manual page is
 available as bzip2.txt.  A statement about Y2K issues is now included
 in the file Y2K_INFO.


 HOW TO BUILD -- UNIX

 Type `make'.  This builds the library libbz2.a and then the
 programs bzip2 and bzip2recover.  Six self-tests are run.
 If the self-tests complete ok, carry on to installation:

 To install in /usr/bin, /usr/lib, /usr/man and /usr/include, type
    make install
 To install somewhere else, eg, /xxx/yyy/{bin,lib,man,include}, type
    make install PREFIX=/xxx/yyy
 If you are (justifiably) paranoid and want to see what 'make install'
 is going to do, you can first do
    make -n install                      or
    make -n install PREFIX=/xxx/yyy      respectively.
 The -n instructs make to show the commands it would execute, but
 not actually execute them.


 HOW TO BUILD -- UNIX, shared library libbz2.so.

 Do 'make -f Makefile-libbz2_so'.  This Makefile seems to work for
 Linux-ELF (RedHat 5.2 on an x86 box), with gcc.  I make no claims
 that it works for any other platform, though I suspect it probably
 will work for most platforms employing both ELF and gcc.

 bzip2-shared, a client of the shared library, is also build, but
 not self-tested.  So I suggest you also build using the normal
 Makefile, since that conducts a self-test.

 Important note for people upgrading .so's from 0.9.0/0.9.5 to
 version 1.0.  All the functions in the library have been renamed,
 from (eg) bzCompress to BZ2_bzCompress, to avoid namespace pollution.
 Unfortunately this means that the libbz2.so created by
 Makefile-libbz2_so will not work with any program which used an
 older version of the library.  Sorry.  I do encourage library
 clients to make the effort to upgrade to use version 1.0, since
 it is both faster and more robust than previous versions.


 HOW TO BUILD -- Windows 95, NT, DOS, Mac, etc.

 It's difficult for me to support compilation on all these platforms.
 My approach is to collect binaries for these platforms, and put them
 on the master web page (http://sourceware.cygnus.com/bzip2).  Look
 there.  However (FWIW), bzip2-1.0 is very standard ANSI C and should
 compile unmodified with MS Visual C.  For Win32, there is one
 important caveat: in bzip2.c, you must set BZ_UNIX to 0 and
 BZ_LCCWIN32 to 1 before building.  If you have difficulties building,
 you might want to read README.COMPILATION.PROBLEMS.


 VALIDATION

 Correct operation, in the sense that a compressed file can always be
 decompressed to reproduce the original, is obviously of paramount
 importance.  To validate bzip2, I used a modified version of Mark
 Nelson's churn program.  Churn is an automated test driver which
 recursively traverses a directory structure, using bzip2 to compress
 and then decompress each file it encounters, and checking that the
 decompressed data is the same as the original.  There are more details
 in Section 4 of the user guide.


 Please read and be aware of the following:

 WARNING:

    This program (attempts to) compress data by performing several
    non-trivial transformations on it.  Unless you are 100% familiar
    with *all* the algorithms contained herein, and with the
    consequences of modifying them, you should NOT meddle with the
    compression or decompression machinery.  Incorrect changes can and
    very likely *will* lead to disastrous loss of data.


 DISCLAIMER:

    I TAKE NO RESPONSIBILITY FOR ANY LOSS OF DATA ARISING FROM THE
    USE OF THIS PROGRAM, HOWSOEVER CAUSED.

    Every compression of a file implies an assumption that the
    compressed file can be decompressed to reproduce the original.
    Great efforts in design, coding and testing have been made to
    ensure that this program works correctly.  However, the complexity
    of the algorithms, and, in particular, the presence of various
    special cases in the code which occur with very low but non-zero
    probability make it impossible to rule out the possibility of bugs
    remaining in the program.  DO NOT COMPRESS ANY DATA WITH THIS
    PROGRAM UNLESS YOU ARE PREPARED TO ACCEPT THE POSSIBILITY, HOWEVER
    SMALL, THAT THE DATA WILL NOT BE RECOVERABLE.

    That is not to say this program is inherently unreliable.  Indeed,
    I very much hope the opposite is true.  bzip2 has been carefully
    constructed and extensively tested.


 PATENTS:

    To the best of my knowledge, bzip2 does not use any patented
    algorithms.  However, I do not have the resources available to
    carry out a full patent search.  Therefore I cannot give any
    guarantee of the above statement.

 End of legalities.


 WHAT'S NEW IN 0.9.0 (as compared to 0.1pl2) ?

    * Approx 10% faster compression, 30% faster decompression
    * -t (test mode) is a lot quicker
    * Can decompress concatenated compressed files
    * Programming interface, so programs can directly read/write .bz2 files
    * Less restrictive (BSD-style) licensing
    * Flag handling more compatible with GNU gzip
    * Much more documentation, i.e., a proper user manual
    * Hopefully, improved portability (at least of the library)

 WHAT'S NEW IN 0.9.5 ?

    * Compression speed is much less sensitive to the input
      data than in previous versions.  Specifically, the very
      slow performance caused by repetitive data is fixed.
    * Many small improvements in file and flag handling.
    * A Y2K statement.

 WHAT'S NEW IN 1.0

    See the CHANGES file.

 I hope you find bzip2 useful.  Feel free to contact me at
    jseward@acm.org
 if you have any suggestions or queries.  Many people mailed me with
 comments, suggestions and patches after the releases of bzip-0.15,
 bzip-0.21, bzip2-0.1pl2 and bzip2-0.9.0, and the changes in bzip2 are
 largely a result of this feedback.  I thank you for your comments.

 At least for the time being, bzip2's "home" is (or can be reached via)
 http://www.muraroa.demon.co.uk.

 Julian Seward
 jseward@acm.org

 Cambridge, UK
 18   July 1996 (version 0.15)
 25 August 1996 (version 0.21)
  7 August 1997 (bzip2, version 0.1)
 29 August 1997 (bzip2, version 0.1pl2)
 23 August 1998 (bzip2, version 0.9.0)
  8   June 1999 (bzip2, version 0.9.5)
  4   Sept 1999 (bzip2, version 0.9.5d)
  5    May 2000 (bzip2, version 1.0pre8)

	This is the README for bzip2, a block-sorting file compressor, version
	1.0. This version is fully compatible with the previous public
	releases, bzip2-0.1pl2, bzip2-0.9.0 and bzip2-0.9.5.

	bzip2-1.0 is distributed under a BSD-style license. For details,
	see the file LICENSE.

	Complete documentation is available in Postscript form (manual.ps) or
	html (manual_toc.html). A plain-text version of the manual page is
	available as bzip2.txt. A statement about Y2K issues is now included
	in the file Y2K_INFO.


	HOW TO BUILD -- UNIX

	Type `make'. This builds the library libbz2.a and then the
	programs bzip2 and bzip2recover. Six self-tests are run.
	If the self-tests complete ok, carry on to installation:

	To install in /usr/bin, /usr/lib, /usr/man and /usr/include, type
	make install
	To install somewhere else, eg, /xxx/yyy/{bin,lib,man,include}, type
	make install PREFIX=/xxx/yyy
	If you are (justifiably) paranoid and want to see what 'make install'
	is going to do, you can first do
	make -n install or
	make -n install PREFIX=/xxx/yyy respectively.
	The -n instructs make to show the commands it would execute, but
	not actually execute them.


	HOW TO BUILD -- UNIX, shared library libbz2.so.

	Do 'make -f Makefile-libbz2_so'. This Makefile seems to work for
	Linux-ELF (RedHat 5.2 on an x86 box), with gcc. I make no claims
	that it works for any other platform, though I suspect it probably
	will work for most platforms employing both ELF and gcc.

	bzip2-shared, a client of the shared library, is also build, but
	not self-tested. So I suggest you also build using the normal
	Makefile, since that conducts a self-test.

	Important note for people upgrading .so's from 0.9.0/0.9.5 to
	version 1.0. All the functions in the library have been renamed,
	from (eg) bzCompress to BZ2_bzCompress, to avoid namespace pollution.
	Unfortunately this means that the libbz2.so created by
	Makefile-libbz2_so will not work with any program which used an
	older version of the library. Sorry. I do encourage library
	clients to make the effort to upgrade to use version 1.0, since
	it is both faster and more robust than previous versions.


	HOW TO BUILD -- Windows 95, NT, DOS, Mac, etc.

	It's difficult for me to support compilation on all these platforms.
	My approach is to collect binaries for these platforms, and put them
	on the master web page (http://sourceware.cygnus.com/bzip2). Look
	there. However (FWIW), bzip2-1.0 is very standard ANSI C and should
	compile unmodified with MS Visual C. For Win32, there is one
	important caveat: in bzip2.c, you must set BZ_UNIX to 0 and
	BZ_LCCWIN32 to 1 before building. If you have difficulties building,
	you might want to read README.COMPILATION.PROBLEMS.


	VALIDATION

	Correct operation, in the sense that a compressed file can always be
	decompressed to reproduce the original, is obviously of paramount
	importance. To validate bzip2, I used a modified version of Mark
	Nelson's churn program. Churn is an automated test driver which
	recursively traverses a directory structure, using bzip2 to compress
	and then decompress each file it encounters, and checking that the
	decompressed data is the same as the original. There are more details
	in Section 4 of the user guide.



	Please read and be aware of the following:

	WARNING:

	This program (attempts to) compress data by performing several
	non-trivial transformations on it. Unless you are 100% familiar
	with all the algorithms contained herein, and with the
	consequences of modifying them, you should NOT meddle with the
	compression or decompression machinery. Incorrect changes can and
	very likely will lead to disastrous loss of data.


	DISCLAIMER:

	I TAKE NO RESPONSIBILITY FOR ANY LOSS OF DATA ARISING FROM THE
	USE OF THIS PROGRAM, HOWSOEVER CAUSED.

	Every compression of a file implies an assumption that the
	compressed file can be decompressed to reproduce the original.
	Great efforts in design, coding and testing have been made to
	ensure that this program works correctly. However, the complexity
	of the algorithms, and, in particular, the presence of various
	special cases in the code which occur with very low but non-zero
	probability make it impossible to rule out the possibility of bugs
	remaining in the program. DO NOT COMPRESS ANY DATA WITH THIS
	PROGRAM UNLESS YOU ARE PREPARED TO ACCEPT THE POSSIBILITY, HOWEVER
	SMALL, THAT THE DATA WILL NOT BE RECOVERABLE.

	That is not to say this program is inherently unreliable. Indeed,
	I very much hope the opposite is true. bzip2 has been carefully
	constructed and extensively tested.


	PATENTS:

	To the best of my knowledge, bzip2 does not use any patented
	algorithms. However, I do not have the resources available to
	carry out a full patent search. Therefore I cannot give any
	guarantee of the above statement.

	End of legalities.


	WHAT'S NEW IN 0.9.0 (as compared to 0.1pl2) ?

	* Approx 10% faster compression, 30% faster decompression
	* -t (test mode) is a lot quicker
	* Can decompress concatenated compressed files
	* Programming interface, so programs can directly read/write .bz2 files
	* Less restrictive (BSD-style) licensing
	* Flag handling more compatible with GNU gzip
	* Much more documentation, i.e., a proper user manual
	* Hopefully, improved portability (at least of the library)

	WHAT'S NEW IN 0.9.5 ?

	* Compression speed is much less sensitive to the input
	data than in previous versions. Specifically, the very
	slow performance caused by repetitive data is fixed.
	* Many small improvements in file and flag handling.
	* A Y2K statement.

	WHAT'S NEW IN 1.0

	See the CHANGES file.

	I hope you find bzip2 useful. Feel free to contact me at
	jseward@acm.org
	if you have any suggestions or queries. Many people mailed me with
	comments, suggestions and patches after the releases of bzip-0.15,
	bzip-0.21, bzip2-0.1pl2 and bzip2-0.9.0, and the changes in bzip2 are
	largely a result of this feedback. I thank you for your comments.

	At least for the time being, bzip2's "home" is (or can be reached via)
	http://www.muraroa.demon.co.uk.

	Julian Seward
	jseward@acm.org

	Cambridge, UK
	18 July 1996 (version 0.15)
	25 August 1996 (version 0.21)
	7 August 1997 (bzip2, version 0.1)
	29 August 1997 (bzip2, version 0.1pl2)
	23 August 1998 (bzip2, version 0.9.0)
	8 June 1999 (bzip2, version 0.9.5)
	4 Sept 1999 (bzip2, version 0.9.5d)
	5 May 2000 (bzip2, version 1.0pre8)