This is the README for bzip2/libzip2. This version is fully compatible with the previous public releases.

This file is part of bzip2/libbzip2, a program and library for lossless, block-sorting data compression.

bzip2/libbzip2 version 1.0.8 of 13 July 2019 Copyright (C) 1996-2019 Julian Seward [email protected]

Please read the WARNING, DISCLAIMER and PATENTS sections in this file.

This program is released under the terms of the license contained in 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.

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/local/bin, /usr/local/lib, /usr/local/man and /usr/local/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. 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 site (https://sourceware.org/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 and library (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/LIBRARY, 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/libbzip2 has been carefully constructed and extensively tested.

PATENTS:

To the best of my knowledge, bzip2/libbzip2 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.

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.x ?

See the CHANGES file.

I hope you find bzip2 useful. Feel free to contact the developers at [email protected] 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, 1.0.2 and 1.0.3, and the changes in bzip2 are largely a result of this feedback. I thank you for your comments.

bzip2's "home" is https://sourceware.org/bzip2/

Julian Seward [email protected] 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) 20 December 2006 (bzip2, version 1.0.4) 10 December 2007 (bzip2, version 1.0.5) 6 Sept 2010 (bzip2, version 1.0.6) 27 June 2019 (bzip2, version 1.0.7) 13 July 2019 (bzip2, version 1.0.8)