

This is the README for bzip2, a block-sorting file compressor, version

1.0.3.  This version is fully compatible with the previous public

releases, versions 0.1pl2, 0.9.0, 0.9.5, 1.0.0, 1.0.1 and 1.0.2.



bzip2-1.0.3 is distributed under a BSD-style license.  For details,

see the file LICENSE.



Complete documentation is available in Postscript form (manual.ps),

PDF (manual.pdf) or html (manual.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 7.2 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 built, but not

self-tested.  So I suggest you also build using the normal Makefile,

since that conducts a self-test.  A second reason to prefer the

version statically linked to the library is that, on x86 platforms,

building shared objects makes a valuable register (%ebx) unavailable

to gcc, resulting in a slowdown of 10%-20%, at least for bzip2.



Important note for people upgrading .so's from 0.9.0/0.9.5 to version

1.0.X.  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://sources.redhat.com/bzip2).  Look there.

However (FWIW), bzip2-1.0.X is very standard ANSI C and should compile

unmodified with MS Visual C.  If you have difficulties building, you

might want to read README.COMPILATION.PROBLEMS.



At least using MS Visual C++ 6, you can build from the unmodified

sources by issuing, in a command shell: 

   nmake -f makefile.msc

(you may need to first run the MSVC-provided script VCVARS32.BAT

 so as to set up paths to the MSVC tools correctly).





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.







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 to carry out

   a 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 1.0.0 ?



   See the CHANGES file.



WHAT'S NEW IN 1.0.2 ?



   See the CHANGES file.



WHAT'S NEW IN 1.0.3 ?



   See the CHANGES file.





I hope you find bzip2 useful.  Feel free to contact me at

   jseward@bzip.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, and bzip2 versions 0.1pl2, 0.9.0, 0.9.5, 1.0.0, 1.0.1 and

1.0.2, 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.bzip.org



Julian Seward

jseward@bzip.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)

30 December 2001 (bzip2, version 1.0.2pre1)

15 February 2005 (bzip2, version 1.0.3)

