1 2This is the README for bzip2, a block-sorting file compressor, version 31.0.2. This version is fully compatible with the previous public 4releases, versions 0.1pl2, 0.9.0, 0.9.5, 1.0.0 and 1.0.1. 5 6bzip2-1.0.2 is distributed under a BSD-style license. For details, 7see the file LICENSE. 8 9Complete documentation is available in Postscript form (manual.ps), 10PDF (manual.pdf, amazingly enough) or html (manual_toc.html). A 11plain-text version of the manual page is available as bzip2.txt. 12A statement about Y2K issues is now included in the file Y2K_INFO. 13 14 15HOW TO BUILD -- UNIX 16 17Type `make'. This builds the library libbz2.a and then the 18programs bzip2 and bzip2recover. Six self-tests are run. 19If the self-tests complete ok, carry on to installation: 20 21To install in /usr/bin, /usr/lib, /usr/man and /usr/include, type 22 make install 23To install somewhere else, eg, /xxx/yyy/{bin,lib,man,include}, type 24 make install PREFIX=/xxx/yyy 25If you are (justifiably) paranoid and want to see what 'make install' 26is going to do, you can first do 27 make -n install or 28 make -n install PREFIX=/xxx/yyy respectively. 29The -n instructs make to show the commands it would execute, but 30not actually execute them. 31 32 33HOW TO BUILD -- UNIX, shared library libbz2.so. 34 35Do 'make -f Makefile-libbz2_so'. This Makefile seems to work for 36Linux-ELF (RedHat 7.2 on an x86 box), with gcc. I make no claims 37that it works for any other platform, though I suspect it probably 38will work for most platforms employing both ELF and gcc. 39 40bzip2-shared, a client of the shared library, is also built, but not 41self-tested. So I suggest you also build using the normal Makefile, 42since that conducts a self-test. A second reason to prefer the 43version statically linked to the library is that, on x86 platforms, 44building shared objects makes a valuable register (%ebx) unavailable 45to gcc, resulting in a slowdown of 10%-20%, at least for bzip2. 46 47Important note for people upgrading .so's from 0.9.0/0.9.5 to version 481.0.X. All the functions in the library have been renamed, from (eg) 49bzCompress to BZ2_bzCompress, to avoid namespace pollution. 50Unfortunately this means that the libbz2.so created by 51Makefile-libbz2_so will not work with any program which used an older 52version of the library. Sorry. I do encourage library clients to 53make the effort to upgrade to use version 1.0, since it is both faster 54and more robust than previous versions. 55 56 57HOW TO BUILD -- Windows 95, NT, DOS, Mac, etc. 58 59It's difficult for me to support compilation on all these platforms. 60My approach is to collect binaries for these platforms, and put them 61on the master web page (http://sources.redhat.com/bzip2). Look there. 62However (FWIW), bzip2-1.0.X is very standard ANSI C and should compile 63unmodified with MS Visual C. If you have difficulties building, you 64might want to read README.COMPILATION.PROBLEMS. 65 66At least using MS Visual C++ 6, you can build from the unmodified 67sources by issuing, in a command shell: 68 nmake -f makefile.msc 69(you may need to first run the MSVC-provided script VCVARS32.BAT 70 so as to set up paths to the MSVC tools correctly). 71 72 73VALIDATION 74 75Correct operation, in the sense that a compressed file can always be 76decompressed to reproduce the original, is obviously of paramount 77importance. To validate bzip2, I used a modified version of Mark 78Nelson's churn program. Churn is an automated test driver which 79recursively traverses a directory structure, using bzip2 to compress 80and then decompress each file it encounters, and checking that the 81decompressed data is the same as the original. There are more details 82in Section 4 of the user guide. 83 84 85 86Please read and be aware of the following: 87 88WARNING: 89 90 This program (attempts to) compress data by performing several 91 non-trivial transformations on it. Unless you are 100% familiar 92 with *all* the algorithms contained herein, and with the 93 consequences of modifying them, you should NOT meddle with the 94 compression or decompression machinery. Incorrect changes can and 95 very likely *will* lead to disastrous loss of data. 96 97 98DISCLAIMER: 99 100 I TAKE NO RESPONSIBILITY FOR ANY LOSS OF DATA ARISING FROM THE 101 USE OF THIS PROGRAM, HOWSOEVER CAUSED. 102 103 Every compression of a file implies an assumption that the 104 compressed file can be decompressed to reproduce the original. 105 Great efforts in design, coding and testing have been made to 106 ensure that this program works correctly. However, the complexity 107 of the algorithms, and, in particular, the presence of various 108 special cases in the code which occur with very low but non-zero 109 probability make it impossible to rule out the possibility of bugs 110 remaining in the program. DO NOT COMPRESS ANY DATA WITH THIS 111 PROGRAM UNLESS YOU ARE PREPARED TO ACCEPT THE POSSIBILITY, HOWEVER 112 SMALL, THAT THE DATA WILL NOT BE RECOVERABLE. 113 114 That is not to say this program is inherently unreliable. Indeed, 115 I very much hope the opposite is true. bzip2 has been carefully 116 constructed and extensively tested. 117 118 119PATENTS: 120 121 To the best of my knowledge, bzip2 does not use any patented 122 algorithms. However, I do not have the resources available to 123 carry out a full patent search. Therefore I cannot give any 124 guarantee of the above statement. 125 126End of legalities. 127 128 129WHAT'S NEW IN 0.9.0 (as compared to 0.1pl2) ? 130 131 * Approx 10% faster compression, 30% faster decompression 132 * -t (test mode) is a lot quicker 133 * Can decompress concatenated compressed files 134 * Programming interface, so programs can directly read/write .bz2 files 135 * Less restrictive (BSD-style) licensing 136 * Flag handling more compatible with GNU gzip 137 * Much more documentation, i.e., a proper user manual 138 * Hopefully, improved portability (at least of the library) 139 140WHAT'S NEW IN 0.9.5 ? 141 142 * Compression speed is much less sensitive to the input 143 data than in previous versions. Specifically, the very 144 slow performance caused by repetitive data is fixed. 145 * Many small improvements in file and flag handling. 146 * A Y2K statement. 147 148WHAT'S NEW IN 1.0.0 ? 149 150 See the CHANGES file. 151 152WHAT'S NEW IN 1.0.2 ? 153 154 See the CHANGES file. 155 156 157I hope you find bzip2 useful. Feel free to contact me at 158 jseward@acm.org 159if you have any suggestions or queries. Many people mailed me with 160comments, suggestions and patches after the releases of bzip-0.15, 161bzip-0.21, and bzip2 versions 0.1pl2, 0.9.0, 0.9.5, 1.0.0 and 1.0.1, 162and the changes in bzip2 are largely a result of this feedback. 163I thank you for your comments. 164 165At least for the time being, bzip2's "home" is (or can be reached via) 166http://sources.redhat.com/bzip2. 167 168Julian Seward 169jseward@acm.org 170 171Cambridge, UK (and what a great town this is!) 172 17318 July 1996 (version 0.15) 17425 August 1996 (version 0.21) 175 7 August 1997 (bzip2, version 0.1) 17629 August 1997 (bzip2, version 0.1pl2) 17723 August 1998 (bzip2, version 0.9.0) 178 8 June 1999 (bzip2, version 0.9.5) 179 4 Sept 1999 (bzip2, version 0.9.5d) 180 5 May 2000 (bzip2, version 1.0pre8) 18130 December 2001 (bzip2, version 1.0.2pre1)