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1 This is the README for bzip2/libzip2.
2 This version is fully compatible with the previous public releases.
3
4 ------------------------------------------------------------------
5 This file is part of bzip2/libbzip2, a program and library for
6 lossless, block-sorting data compression.
7
8 bzip2/libbzip2 version 1.0.4 of 20 December 2006
9 Copyright (C) 1996-2006 Julian Seward <jseward@bzip.org>
10
11 Please read the WARNING, DISCLAIMER and PATENTS sections in this file.
12
13 This program is released under the terms of the license contained
14 in the file LICENSE.
15 ------------------------------------------------------------------
16
17 Complete documentation is available in Postscript form (manual.ps),
18 PDF (manual.pdf) or html (manual.html). A plain-text version of the
19 manual page is available as bzip2.txt.
20
21
22 HOW TO BUILD -- UNIX
23
24 Type 'make'. This builds the library libbz2.a and then the programs
25 bzip2 and bzip2recover. Six self-tests are run. If the self-tests
26 complete ok, carry on to installation:
27
28 To install in /usr/local/bin, /usr/local/lib, /usr/local/man and
29 /usr/local/include, type
30
31 make install
32
33 To install somewhere else, eg, /xxx/yyy/{bin,lib,man,include}, type
34
35 make install PREFIX=/xxx/yyy
36
37 If you are (justifiably) paranoid and want to see what 'make install'
38 is going to do, you can first do
39
40 make -n install or
41 make -n install PREFIX=/xxx/yyy respectively.
42
43 The -n instructs make to show the commands it would execute, but not
44 actually execute them.
45
46
47 HOW TO BUILD -- UNIX, shared library libbz2.so.
48
49 Do 'make -f Makefile-libbz2_so'. This Makefile seems to work for
50 Linux-ELF (RedHat 7.2 on an x86 box), with gcc. I make no claims
51 that it works for any other platform, though I suspect it probably
52 will work for most platforms employing both ELF and gcc.
53
54 bzip2-shared, a client of the shared library, is also built, but not
55 self-tested. So I suggest you also build using the normal Makefile,
56 since that conducts a self-test. A second reason to prefer the
57 version statically linked to the library is that, on x86 platforms,
58 building shared objects makes a valuable register (%ebx) unavailable
59 to gcc, resulting in a slowdown of 10%-20%, at least for bzip2.
60
61 Important note for people upgrading .so's from 0.9.0/0.9.5 to version
62 1.0.X. All the functions in the library have been renamed, from (eg)
63 bzCompress to BZ2_bzCompress, to avoid namespace pollution.
64 Unfortunately this means that the libbz2.so created by
65 Makefile-libbz2_so will not work with any program which used an older
66 version of the library. I do encourage library clients to make the
67 effort to upgrade to use version 1.0, since it is both faster and more
68 robust than previous versions.
69
70
71 HOW TO BUILD -- Windows 95, NT, DOS, Mac, etc.
72
73 It's difficult for me to support compilation on all these platforms.
74 My approach is to collect binaries for these platforms, and put them
75 on the master web site (http://www.bzip.org). Look there. However
76 (FWIW), bzip2-1.0.X is very standard ANSI C and should compile
77 unmodified with MS Visual C. If you have difficulties building, you
78 might want to read README.COMPILATION.PROBLEMS.
79
80 At least using MS Visual C++ 6, you can build from the unmodified
81 sources by issuing, in a command shell:
82
83 nmake -f makefile.msc
84
85 (you may need to first run the MSVC-provided script VCVARS32.BAT
86 so as to set up paths to the MSVC tools correctly).
87
88
89 VALIDATION
90
91 Correct operation, in the sense that a compressed file can always be
92 decompressed to reproduce the original, is obviously of paramount
93 importance. To validate bzip2, I used a modified version of Mark
94 Nelson's churn program. Churn is an automated test driver which
95 recursively traverses a directory structure, using bzip2 to compress
96 and then decompress each file it encounters, and checking that the
97 decompressed data is the same as the original.
98
99
100
101 Please read and be aware of the following:
102
103 WARNING:
104
105 This program and library (attempts to) compress data by
106 performing several non-trivial transformations on it.
107 Unless you are 100% familiar with *all* the algorithms
108 contained herein, and with the consequences of modifying them,
109 you should NOT meddle with the compression or decompression
110 machinery. Incorrect changes can and very likely *will*
111 lead to disastrous loss of data.
112
113
114 DISCLAIMER:
115
116 I TAKE NO RESPONSIBILITY FOR ANY LOSS OF DATA ARISING FROM THE
117 USE OF THIS PROGRAM/LIBRARY, HOWSOEVER CAUSED.
118
119 Every compression of a file implies an assumption that the
120 compressed file can be decompressed to reproduce the original.
121 Great efforts in design, coding and testing have been made to
122 ensure that this program works correctly. However, the complexity
123 of the algorithms, and, in particular, the presence of various
124 special cases in the code which occur with very low but non-zero
125 probability make it impossible to rule out the possibility of bugs
126 remaining in the program. DO NOT COMPRESS ANY DATA WITH THIS
127 PROGRAM UNLESS YOU ARE PREPARED TO ACCEPT THE POSSIBILITY, HOWEVER
128 SMALL, THAT THE DATA WILL NOT BE RECOVERABLE.
129
130 That is not to say this program is inherently unreliable.
131 Indeed, I very much hope the opposite is true. bzip2/libbzip2
132 has been carefully constructed and extensively tested.
133
134
135 PATENTS:
136
137 To the best of my knowledge, bzip2/libbzip2 does not use any
138 patented algorithms. However, I do not have the resources
139 to carry out a patent search. Therefore I cannot give any
140 guarantee of the above statement.
141
142
143
144 WHAT'S NEW IN 0.9.0 (as compared to 0.1pl2) ?
145
146 * Approx 10% faster compression, 30% faster decompression
147 * -t (test mode) is a lot quicker
148 * Can decompress concatenated compressed files
149 * Programming interface, so programs can directly read/write .bz2 files
150 * Less restrictive (BSD-style) licensing
151 * Flag handling more compatible with GNU gzip
152 * Much more documentation, i.e., a proper user manual
153 * Hopefully, improved portability (at least of the library)
154
155 WHAT'S NEW IN 0.9.5 ?
156
157 * Compression speed is much less sensitive to the input
158 data than in previous versions. Specifically, the very
159 slow performance caused by repetitive data is fixed.
160 * Many small improvements in file and flag handling.
161 * A Y2K statement.
162
163 WHAT'S NEW IN 1.0.0 ?
164
165 See the CHANGES file.
166
167 WHAT'S NEW IN 1.0.2 ?
168
169 See the CHANGES file.
170
171 WHAT'S NEW IN 1.0.3 ?
172
173 See the CHANGES file.
174
175 WHAT'S NEW IN 1.0.4 ?
176
177 See the CHANGES file.
178
179
180 I hope you find bzip2 useful. Feel free to contact me at
181 jseward@bzip.org
182 if you have any suggestions or queries. Many people mailed me with
183 comments, suggestions and patches after the releases of bzip-0.15,
184 bzip-0.21, and bzip2 versions 0.1pl2, 0.9.0, 0.9.5, 1.0.0, 1.0.1,
185 1.0.2 and 1.0.3, and the changes in bzip2 are largely a result of this
186 feedback. I thank you for your comments.
187
188 bzip2's "home" is http://www.bzip.org/
189
190 Julian Seward
191 jseward@bzip.org
192 Cambridge, UK.
193
194 18 July 1996 (version 0.15)
195 25 August 1996 (version 0.21)
196 7 August 1997 (bzip2, version 0.1)
197 29 August 1997 (bzip2, version 0.1pl2)
198 23 August 1998 (bzip2, version 0.9.0)
199 8 June 1999 (bzip2, version 0.9.5)
200 4 Sept 1999 (bzip2, version 0.9.5d)
201 5 May 2000 (bzip2, version 1.0pre8)
202 30 December 2001 (bzip2, version 1.0.2pre1)
203 15 February 2005 (bzip2, version 1.0.3)
204 20 December 2006 (bzip2, version 1.0.4)

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