1
2This is the README for bzip2, a block-sorting file compressor, version
31.0. This version is fully compatible with the previous public
4releases, bzip2-0.1pl2, bzip2-0.9.0 and bzip2-0.9.5.
5
6bzip2-1.0 is distributed under a BSD-style license. For details,
7see the file LICENSE.
8
9Complete documentation is available in Postscript form (manual.ps) or
10html (manual_toc.html). A plain-text version of the manual page is
11available as bzip2.txt. A statement about Y2K issues is now included
12in 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 5.2 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 build, but
41not self-tested. So I suggest you also build using the normal
42Makefile, since that conducts a self-test.
43
44Important note for people upgrading .so's from 0.9.0/0.9.5 to
45version 1.0. All the functions in the library have been renamed,
46from (eg) bzCompress to BZ2_bzCompress, to avoid namespace pollution.
47Unfortunately this means that the libbz2.so created by
48Makefile-libbz2_so will not work with any program which used an
49older version of the library. Sorry. I do encourage library
50clients to make the effort to upgrade to use version 1.0, since
51it is both faster and more robust than previous versions.
52
53
54HOW TO BUILD -- Windows 95, NT, DOS, Mac, etc.
55
56It's difficult for me to support compilation on all these platforms.
57My approach is to collect binaries for these platforms, and put them
58on the master web page (http://sourceware.cygnus.com/bzip2). Look
59there. However (FWIW), bzip2-1.0 is very standard ANSI C and should
60compile unmodified with MS Visual C. For Win32, there is one
61important caveat: in bzip2.c, you must set BZ_UNIX to 0 and
62BZ_LCCWIN32 to 1 before building. If you have difficulties building,
63you might want to read README.COMPILATION.PROBLEMS.
64
65
66VALIDATION
67
68Correct operation, in the sense that a compressed file can always be
69decompressed to reproduce the original, is obviously of paramount
70importance. To validate bzip2, I used a modified version of Mark
71Nelson's churn program. Churn is an automated test driver which
72recursively traverses a directory structure, using bzip2 to compress
73and then decompress each file it encounters, and checking that the
74decompressed data is the same as the original. There are more details
75in Section 4 of the user guide.
76
77
78
79Please read and be aware of the following:
80
81WARNING:
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
91DISCLAIMER:
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
112PATENTS:
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
119End of legalities.
120
121
122WHAT'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
133WHAT'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
141WHAT'S NEW IN 1.0
142
143 See the CHANGES file.
144
145I hope you find bzip2 useful. Feel free to contact me at
146 jseward@acm.org
147if you have any suggestions or queries. Many people mailed me with
148comments, suggestions and patches after the releases of bzip-0.15,
149bzip-0.21, bzip2-0.1pl2 and bzip2-0.9.0, and the changes in bzip2 are
150largely a result of this feedback. I thank you for your comments.
151
152At least for the time being, bzip2's "home" is (or can be reached via)
153http://www.muraroa.demon.co.uk.
154
155Julian Seward
156jseward@acm.org
157
158Cambridge, UK
15918 July 1996 (version 0.15)
16025 August 1996 (version 0.21)
161 7 August 1997 (bzip2, version 0.1)
16229 August 1997 (bzip2, version 0.1pl2)
16323 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)
167