README (6510B)
1 2 This is the README for bzip2, a block-sorting file compressor, version 3 1.0. This version is fully compatible with the previous public 4 releases, bzip2-0.1pl2, bzip2-0.9.0 and bzip2-0.9.5. 5 6 bzip2-1.0 is distributed under a BSD-style license. For details, 7 see the file LICENSE. 8 9 Complete documentation is available in Postscript form (manual.ps) or 10 html (manual_toc.html). A plain-text version of the manual page is 11 available as bzip2.txt. A statement about Y2K issues is now included 12 in the file Y2K_INFO. 13 14 15 HOW TO BUILD -- UNIX 16 17 Type `make'. This builds the library libbz2.a and then the 18 programs bzip2 and bzip2recover. Six self-tests are run. 19 If the self-tests complete ok, carry on to installation: 20 21 To install in /usr/bin, /usr/lib, /usr/man and /usr/include, type 22 make install 23 To install somewhere else, eg, /xxx/yyy/{bin,lib,man,include}, type 24 make install PREFIX=/xxx/yyy 25 If you are (justifiably) paranoid and want to see what 'make install' 26 is going to do, you can first do 27 make -n install or 28 make -n install PREFIX=/xxx/yyy respectively. 29 The -n instructs make to show the commands it would execute, but 30 not actually execute them. 31 32 33 HOW TO BUILD -- UNIX, shared library libbz2.so. 34 35 Do 'make -f Makefile-libbz2_so'. This Makefile seems to work for 36 Linux-ELF (RedHat 5.2 on an x86 box), with gcc. I make no claims 37 that it works for any other platform, though I suspect it probably 38 will work for most platforms employing both ELF and gcc. 39 40 bzip2-shared, a client of the shared library, is also build, but 41 not self-tested. So I suggest you also build using the normal 42 Makefile, since that conducts a self-test. 43 44 Important note for people upgrading .so's from 0.9.0/0.9.5 to 45 version 1.0. All the functions in the library have been renamed, 46 from (eg) bzCompress to BZ2_bzCompress, to avoid namespace pollution. 47 Unfortunately this means that the libbz2.so created by 48 Makefile-libbz2_so will not work with any program which used an 49 older version of the library. Sorry. I do encourage library 50 clients to make the effort to upgrade to use version 1.0, since 51 it is both faster and more robust than previous versions. 52 53 54 HOW TO BUILD -- Windows 95, NT, DOS, Mac, etc. 55 56 It's difficult for me to support compilation on all these platforms. 57 My approach is to collect binaries for these platforms, and put them 58 on the master web page (http://sourceware.cygnus.com/bzip2). Look 59 there. However (FWIW), bzip2-1.0 is very standard ANSI C and should 60 compile unmodified with MS Visual C. For Win32, there is one 61 important caveat: in bzip2.c, you must set BZ_UNIX to 0 and 62 BZ_LCCWIN32 to 1 before building. If you have difficulties building, 63 you might want to read README.COMPILATION.PROBLEMS. 64 65 66 VALIDATION 67 68 Correct operation, in the sense that a compressed file can always be 69 decompressed to reproduce the original, is obviously of paramount 70 importance. To validate bzip2, I used a modified version of Mark 71 Nelson's churn program. Churn is an automated test driver which 72 recursively traverses a directory structure, using bzip2 to compress 73 and then decompress each file it encounters, and checking that the 74 decompressed data is the same as the original. There are more details 75 in Section 4 of the user guide. 76 77 78 79 Please read and be aware of the following: 80 81 WARNING: 82 83 This program (attempts to) compress data by performing several 84 non-trivial transformations on it. Unless you are 100% familiar 85 with *all* the algorithms contained herein, and with the 86 consequences of modifying them, you should NOT meddle with the 87 compression or decompression machinery. Incorrect changes can and 88 very likely *will* lead to disastrous loss of data. 89 90 91 DISCLAIMER: 92 93 I TAKE NO RESPONSIBILITY FOR ANY LOSS OF DATA ARISING FROM THE 94 USE OF THIS PROGRAM, HOWSOEVER CAUSED. 95 96 Every compression of a file implies an assumption that the 97 compressed file can be decompressed to reproduce the original. 98 Great efforts in design, coding and testing have been made to 99 ensure that this program works correctly. However, the complexity 100 of the algorithms, and, in particular, the presence of various 101 special cases in the code which occur with very low but non-zero 102 probability make it impossible to rule out the possibility of bugs 103 remaining in the program. DO NOT COMPRESS ANY DATA WITH THIS 104 PROGRAM UNLESS YOU ARE PREPARED TO ACCEPT THE POSSIBILITY, HOWEVER 105 SMALL, THAT THE DATA WILL NOT BE RECOVERABLE. 106 107 That is not to say this program is inherently unreliable. Indeed, 108 I very much hope the opposite is true. bzip2 has been carefully 109 constructed and extensively tested. 110 111 112 PATENTS: 113 114 To the best of my knowledge, bzip2 does not use any patented 115 algorithms. However, I do not have the resources available to 116 carry out a full patent search. Therefore I cannot give any 117 guarantee of the above statement. 118 119 End of legalities. 120 121 122 WHAT'S NEW IN 0.9.0 (as compared to 0.1pl2) ? 123 124 * Approx 10% faster compression, 30% faster decompression 125 * -t (test mode) is a lot quicker 126 * Can decompress concatenated compressed files 127 * Programming interface, so programs can directly read/write .bz2 files 128 * Less restrictive (BSD-style) licensing 129 * Flag handling more compatible with GNU gzip 130 * Much more documentation, i.e., a proper user manual 131 * Hopefully, improved portability (at least of the library) 132 133 WHAT'S NEW IN 0.9.5 ? 134 135 * Compression speed is much less sensitive to the input 136 data than in previous versions. Specifically, the very 137 slow performance caused by repetitive data is fixed. 138 * Many small improvements in file and flag handling. 139 * A Y2K statement. 140 141 WHAT'S NEW IN 1.0 142 143 See the CHANGES file. 144 145 I hope you find bzip2 useful. Feel free to contact me at 146 jseward@acm.org 147 if you have any suggestions or queries. Many people mailed me with 148 comments, suggestions and patches after the releases of bzip-0.15, 149 bzip-0.21, bzip2-0.1pl2 and bzip2-0.9.0, and the changes in bzip2 are 150 largely a result of this feedback. I thank you for your comments. 151 152 At least for the time being, bzip2's "home" is (or can be reached via) 153 http://www.muraroa.demon.co.uk. 154 155 Julian Seward 156 jseward@acm.org 157 158 Cambridge, UK 159 18 July 1996 (version 0.15) 160 25 August 1996 (version 0.21) 161 7 August 1997 (bzip2, version 0.1) 162 29 August 1997 (bzip2, version 0.1pl2) 163 23 August 1998 (bzip2, version 0.9.0) 164 8 June 1999 (bzip2, version 0.9.5) 165 4 Sept 1999 (bzip2, version 0.9.5d) 166 5 May 2000 (bzip2, version 1.0pre8)