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This is the README for bzip2, a block-sorting file compressor, version
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1.0. This version is fully compatible with the previous public
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releases, bzip2-0.1pl2, bzip2-0.9.0 and bzip2-0.9.5.
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bzip2-1.0 is distributed under a BSD-style license. For details,
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see the file LICENSE.
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Complete documentation is available in Postscript form (manual.ps) or
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html (manual_toc.html). A plain-text version of the manual page is
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available as bzip2.txt. A statement about Y2K issues is now included
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in the file Y2K_INFO.
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HOW TO BUILD -- UNIX
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Type `make'. This builds the library libbz2.a and then the
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programs bzip2 and bzip2recover. Six self-tests are run.
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If the self-tests complete ok, carry on to installation:
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To install in /usr/bin, /usr/lib, /usr/man and /usr/include, type
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make install
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To install somewhere else, eg, /xxx/yyy/{bin,lib,man,include}, type
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make install PREFIX=/xxx/yyy
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If you are (justifiably) paranoid and want to see what 'make install'
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is going to do, you can first do
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make -n install or
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make -n install PREFIX=/xxx/yyy respectively.
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The -n instructs make to show the commands it would execute, but
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not actually execute them.
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HOW TO BUILD -- UNIX, shared library libbz2.so.
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Do 'make -f Makefile-libbz2_so'. This Makefile seems to work for
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Linux-ELF (RedHat 5.2 on an x86 box), with gcc. I make no claims
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that it works for any other platform, though I suspect it probably
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will work for most platforms employing both ELF and gcc.
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bzip2-shared, a client of the shared library, is also build, but
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not self-tested. So I suggest you also build using the normal
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Makefile, since that conducts a self-test.
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Important note for people upgrading .so's from 0.9.0/0.9.5 to
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version 1.0. All the functions in the library have been renamed,
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from (eg) bzCompress to BZ2_bzCompress, to avoid namespace pollution.
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Unfortunately this means that the libbz2.so created by
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Makefile-libbz2_so will not work with any program which used an
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older version of the library. Sorry. I do encourage library
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clients to make the effort to upgrade to use version 1.0, since
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it is both faster and more robust than previous versions.
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HOW TO BUILD -- Windows 95, NT, DOS, Mac, etc.
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It's difficult for me to support compilation on all these platforms.
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My approach is to collect binaries for these platforms, and put them
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on the master web page (http://sourceware.cygnus.com/bzip2). Look
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there. However (FWIW), bzip2-1.0 is very standard ANSI C and should
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compile unmodified with MS Visual C. For Win32, there is one
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important caveat: in bzip2.c, you must set BZ_UNIX to 0 and
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BZ_LCCWIN32 to 1 before building. If you have difficulties building,
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you might want to read README.COMPILATION.PROBLEMS.
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VALIDATION
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Correct operation, in the sense that a compressed file can always be
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decompressed to reproduce the original, is obviously of paramount
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importance. To validate bzip2, I used a modified version of Mark
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Nelson's churn program. Churn is an automated test driver which
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recursively traverses a directory structure, using bzip2 to compress
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and then decompress each file it encounters, and checking that the
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decompressed data is the same as the original. There are more details
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in Section 4 of the user guide.
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Please read and be aware of the following:
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WARNING:
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This program (attempts to) compress data by performing several
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non-trivial transformations on it. Unless you are 100% familiar
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with *all* the algorithms contained herein, and with the
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consequences of modifying them, you should NOT meddle with the
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compression or decompression machinery. Incorrect changes can and
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very likely *will* lead to disastrous loss of data.
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DISCLAIMER:
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I TAKE NO RESPONSIBILITY FOR ANY LOSS OF DATA ARISING FROM THE
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USE OF THIS PROGRAM, HOWSOEVER CAUSED.
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Every compression of a file implies an assumption that the
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compressed file can be decompressed to reproduce the original.
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Great efforts in design, coding and testing have been made to
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ensure that this program works correctly. However, the complexity
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of the algorithms, and, in particular, the presence of various
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special cases in the code which occur with very low but non-zero
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probability make it impossible to rule out the possibility of bugs
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remaining in the program. DO NOT COMPRESS ANY DATA WITH THIS
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PROGRAM UNLESS YOU ARE PREPARED TO ACCEPT THE POSSIBILITY, HOWEVER
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SMALL, THAT THE DATA WILL NOT BE RECOVERABLE.
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That is not to say this program is inherently unreliable. Indeed,
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I very much hope the opposite is true. bzip2 has been carefully
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constructed and extensively tested.
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PATENTS:
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To the best of my knowledge, bzip2 does not use any patented
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algorithms. However, I do not have the resources available to
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carry out a full patent search. Therefore I cannot give any
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guarantee of the above statement.
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End of legalities.
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WHAT'S NEW IN 0.9.0 (as compared to 0.1pl2) ?
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* Approx 10% faster compression, 30% faster decompression
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* -t (test mode) is a lot quicker
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* Can decompress concatenated compressed files
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* Programming interface, so programs can directly read/write .bz2 files
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* Less restrictive (BSD-style) licensing
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* Flag handling more compatible with GNU gzip
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* Much more documentation, i.e., a proper user manual
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* Hopefully, improved portability (at least of the library)
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WHAT'S NEW IN 0.9.5 ?
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* Compression speed is much less sensitive to the input
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data than in previous versions. Specifically, the very
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slow performance caused by repetitive data is fixed.
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* Many small improvements in file and flag handling.
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* A Y2K statement.
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WHAT'S NEW IN 1.0
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See the CHANGES file.
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I hope you find bzip2 useful. Feel free to contact me at
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jseward@acm.org
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if you have any suggestions or queries. Many people mailed me with
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comments, suggestions and patches after the releases of bzip-0.15,
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bzip-0.21, bzip2-0.1pl2 and bzip2-0.9.0, and the changes in bzip2 are
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largely a result of this feedback. I thank you for your comments.
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At least for the time being, bzip2's "home" is (or can be reached via)
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http://www.muraroa.demon.co.uk.
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Julian Seward
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jseward@acm.org
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Cambridge, UK
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18 July 1996 (version 0.15)
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25 August 1996 (version 0.21)
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7 August 1997 (bzip2, version 0.1)
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29 August 1997 (bzip2, version 0.1pl2)
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23 August 1998 (bzip2, version 0.9.0)
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8 June 1999 (bzip2, version 0.9.5)
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4 Sept 1999 (bzip2, version 0.9.5d)
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5 May 2000 (bzip2, version 1.0pre8)
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