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comparison miscellany/compress-4.0/README3.0 @ 0:bce86c4163a3

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author kono
date Mon, 18 Apr 2005 23:46:02 +0900
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1 Enclosed is compress version 3.0 with the following changes:
2
3 1. "Block" compression is performed. After the BITS run out, the
4 compression ratio is checked every so often. If it is decreasing,
5 the table is cleared and a new set of substrings are generated.
6
7 This makes the output of compress 3.0 not compatable with that of
8 compress 2.0. However, compress 3.0 still accepts the output of
9 compress 2.0. To generate output that is compatable with compress
10 2.0, use the undocumented "-C" flag.
11
12 2. A quiet "-q" flag has been added for use by the news system.
13
14 3. The character chaining has been deleted and the program now uses
15 hashing. This improves the speed of the program, especially
16 during decompression. Other speed improvements have been made,
17 such as using putc() instead of fwrite().
18
19 4. A large table is used on large machines when a relatively small
20 number of bits is specified. This saves much time when compressing
21 for a 16-bit machine on a 32-bit virtual machine. Note that the
22 speed improvement only occurs when the input file is > 30000
23 characters, and the -b BITS is less than or equal to the cutoff
24 described below.
25
26 Most of these changes were made by James A. Woods (ames!jaw). Thank you
27 James!
28
29 Version 3.0 has been beta tested on many machines.
30
31 To compile compress:
32
33 cc -O -DUSERMEM=usermem -o compress compress.c
34
35 Where "usermem" is the amount of physical user memory available (in bytes).
36 If any physical memory is to be reserved for other processes, put in
37 "-DSACREDMEM sacredmem", where "sacredmem" is the amount to be reserved.
38
39 The difference "usermem-sacredmem" determines the maximum BITS that can be
40 specified, and the cutoff bits where the large+fast table is used.
41
42 memory: at least BITS cutoff
43 ------ -- ----- ---- ------
44 4,718,592 16 13
45 2,621,440 16 12
46 1,572,864 16 11
47 1,048,576 16 10
48 631,808 16 --
49 329,728 15 --
50 178,176 14 --
51 99,328 13 --
52 0 12 --
53
54 The default memory size is 750,000 which gives a maximum BITS=16 and no
55 large+fast table.
56
57 The maximum bits can be overrulled by specifying "-DBITS=bits" at
58 compilation time.
59
60 If your machine doesn't support unsigned characters, define "NO_UCHAR"
61 when compiling.
62
63 If your machine has "int" as 16-bits, define "SHORT_INT" when compiling.
64
65 After compilation, move "compress" to a standard executable location, such
66 as /usr/local. Then:
67 cd /usr/local
68 ln compress uncompress
69 ln compress zcat
70
71 On machines that have a fixed stack size (such as Perkin-Elmer), set the
72 stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer).
73
74 Next, install the manual (compress.l).
75 cp compress.l /usr/man/manl
76 cd /usr/man/manl
77 ln compress.l uncompress.l
78 ln compress.l zcat.l
79
80 - or -
81
82 cp compress.l /usr/man/man1/compress.1
83 cd /usr/man/man1
84 ln compress.1 uncompress.1
85 ln compress.1 zcat.1
86
87 The zmore shell script and manual page are for use on systems that have a
88 "more(1)" program. Install the shell script and the manual page in a "bin"
89 and "man" directory, respectively. If your system doesn't have the
90 "more(1)" program, just skip "zmore".
91
92 regards,
93 petsd!joe
94
95 Here is the README file from the previous version of compress (2.0):
96
97 >Enclosed is compress.c version 2.0 with the following bugs fixed:
98 >
99 >1. The packed files produced by compress are different on different
100 > machines and dependent on the vax sysgen option.
101 > The bug was in the different byte/bit ordering on the
102 > various machines. This has been fixed.
103 >
104 > This version is NOT compatible with the original vax posting
105 > unless the '-DCOMPATIBLE' option is specified to the C
106 > compiler. The original posting has a bug which I fixed,
107 > causing incompatible files. I recommend you NOT to use this
108 > option unless you already have a lot of packed files from
109 > the original posting by thomas.
110 >2. The exit status is not well defined (on some machines) causing the
111 > scripts to fail.
112 > The exit status is now 0,1 or 2 and is documented in
113 > compress.l.
114 >3. The function getopt() is not available in all C libraries.
115 > The function getopt() is no longer referenced by the
116 > program.
117 >4. Error status is not being checked on the fwrite() and fflush() calls.
118 > Fixed.
119 >
120 >The following enhancements have been made:
121 >
122 >1. Added facilities of "compact" into the compress program. "Pack",
123 > "Unpack", and "Pcat" are no longer required (no longer supplied).
124 >2. Installed work around for C compiler bug with "-O".
125 >3. Added a magic number header (\037\235). Put the bits specified
126 > in the file.
127 >4. Added "-f" flag to force overwrite of output file.
128 >5. Added "-c" flag and "zcat" program. 'ln compress zcat' after you
129 > compile.
130 >6. The 'uncompress' script has been deleted; simply
131 > 'ln compress uncompress' after you compile and it will work.
132 >7. Removed extra bit masking for machines that support unsigned
133 > characters. If your machine doesn't support unsigned characters,
134 > define "NO_UCHAR" when compiling.
135 >
136 >Compile "compress.c" with "-O -o compress" flags. Move "compress" to a
137 >standard executable location, such as /usr/local. Then:
138 > cd /usr/local
139 > ln compress uncompress
140 > ln compress zcat
141 >
142 >On machines that have a fixed stack size (such as Perkin-Elmer), set the
143 >stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer).
144 >
145 >Next, install the manual (compress.l).
146 > cp compress.l /usr/man/manl - or -
147 > cp compress.l /usr/man/man1/compress.1
148 >
149 >Here is the README that I sent with my first posting:
150 >
151 >>Enclosed is a modified version of compress.c, along with scripts to make it
152 >>run identically to pack(1), unpack(1), an pcat(1). Here is what I
153 >>(petsd!joe) and a colleague (petsd!peora!srd) did:
154 >>
155 >>1. Removed VAX dependencies.
156 >>2. Changed the struct to separate arrays; saves mucho memory.
157 >>3. Did comparisons in unsigned, where possible. (Faster on Perkin-Elmer.)
158 >>4. Sorted the character next chain and changed the search to stop
159 >>prematurely. This saves a lot on the execution time when compressing.
160 >>
161 >>This version is totally compatible with the original version. Even though
162 >>lint(1) -p has no complaints about compress.c, it won't run on a 16-bit
163 >>machine, due to the size of the arrays.
164 >>
165 >>Here is the README file from the original author:
166 >>
167 >>>Well, with all this discussion about file compression (for news batching
168 >>>in particular) going around, I decided to implement the text compression
169 >>>algorithm described in the June Computer magazine. The author claimed
170 >>>blinding speed and good compression ratios. It's certainly faster than
171 >>>compact (but, then, what wouldn't be), but it's also the same speed as
172 >>>pack, and gets better compression than both of them. On 350K bytes of
173 >>>unix-wizards, compact took about 8 minutes of CPU, pack took about 80
174 >>>seconds, and compress (herein) also took 80 seconds. But, compact and
175 >>>pack got about 30% compression, whereas compress got over 50%. So, I
176 >>>decided I had something, and that others might be interested, too.
177 >>>
178 >>>As is probably true of compact and pack (although I haven't checked),
179 >>>the byte order within a word is probably relevant here, but as long as
180 >>>you stay on a single machine type, you should be ok. (Can anybody
181 >>>elucidate on this?) There are a couple of asm's in the code (extv and
182 >>>insv instructions), so anyone porting it to another machine will have to
183 >>>deal with this anyway (and could probably make it compatible with Vax
184 >>>byte order at the same time). Anyway, I've linted the code (both with
185 >>>and without -p), so it should run elsewhere. Note the longs in the
186 >>>code, you can take these out if you reduce BITS to <= 15.
187 >>>
188 >>>Have fun, and as always, if you make good enhancements, or bug fixes,
189 >>>I'd like to see them.
190 >>>
191 >>>=Spencer (thomas@utah-20, {harpo,hplabs,arizona}!utah-cs!thomas)
192 >>
193 >> regards,
194 >> joe
195 >>
196 >>--
197 >>Full-Name: Joseph M. Orost
198 >>UUCP: ..!{decvax,ucbvax,ihnp4}!vax135!petsd!joe
199 >>US Mail: MS 313; Perkin-Elmer; 106 Apple St; Tinton Falls, NJ 07724
200 >>Phone: (201) 870-5844