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2 @(#)README 8.1 (Berkeley) 6/9/93
4 Compress version 4.0 improvements over 3.0:
5 o compress() speedup (10-50%) by changing division hash to xor
6 o decompress() speedup (5-10%)
7 o Memory requirements reduced (3-30%)
8 o Stack requirements reduced to less than 4kb
9 o Removed 'Big+Fast' compress code (FBITS) because of compress speedup
10 o Portability mods for Z8000 and PC/XT (but not zeus 3.2)
11 o Default to 'quiet' mode
12 o Unification of 'force' flags
13 o Manual page overhaul
14 o Portability enhancement for M_XENIX
15 o Removed text on #else and #endif
16 o Added "-V" switch to print version and options
17 o Added #defines for SIGNED_COMPARE_SLOW
18 o Added Makefile and "usermem" program
19 o Removed all floating point computations
20 o New programs: [deleted]
22 The "usermem" script attempts to determine the maximum process size. Some
23 editing of the script may be necessary (see the comments). [It should work
24 fine on 4.3 bsd.] If you can't get it to work at all, just create file
25 "USERMEM" containing the maximum process size in decimal.
27 The following preprocessor symbols control the compilation of "compress.c":
29 o USERMEM Maximum process memory on the system
30 o SACREDMEM Amount to reserve for other proceses
31 o SIGNED_COMPARE_SLOW Unsigned compare instructions are faster
32 o NO_UCHAR Don't use "unsigned char" types
33 o BITS Overrules default set by USERMEM-SACREDMEM
34 o vax Generate inline assembler
35 o interdata Defines SIGNED_COMPARE_SLOW
36 o M_XENIX Makes arrays < 65536 bytes each
37 o pdp11 BITS=12, NO_UCHAR
38 o z8000 BITS=12
39 o pcxt BITS=12
40 o BSD4_2 Allow long filenames ( > 14 characters) &
41 Call setlinebuf(stderr)
43 The difference "usermem-sacredmem" determines the maximum BITS that can be
44 specified with the "-b" flag.
46 memory: at least BITS
47 ------ -- ----- ----
48 433,484 16
49 229,600 15
50 127,536 14
51 73,464 13
52 0 12
54 The default is BITS=16.
56 The maximum bits can be overrulled by specifying "-DBITS=bits" at
57 compilation time.
59 WARNING: files compressed on a large machine with more bits than allowed by
60 a version of compress on a smaller machine cannot be decompressed! Use the
61 "-b12" flag to generate a file on a large machine that can be uncompressed
62 on a 16-bit machine.
64 The output of compress 4.0 is fully compatible with that of compress 3.0.
65 In other words, the output of compress 4.0 may be fed into uncompress 3.0 or
66 the output of compress 3.0 may be fed into uncompress 4.0.
68 The output of compress 4.0 not compatible with that of
69 compress 2.0. However, compress 4.0 still accepts the output of
70 compress 2.0. To generate output that is compatible with compress
71 2.0, use the undocumented "-C" flag.
73 -from mod.sources, submitted by vax135!petsd!joe (Joe Orost), 8/1/85
74 --------------------------------
76 Enclosed is compress version 3.0 with the following changes:
78 1. "Block" compression is performed. After the BITS run out, the
79 compression ratio is checked every so often. If it is decreasing,
80 the table is cleared and a new set of substrings are generated.
82 This makes the output of compress 3.0 not compatible with that of
83 compress 2.0. However, compress 3.0 still accepts the output of
84 compress 2.0. To generate output that is compatible with compress
85 2.0, use the undocumented "-C" flag.
87 2. A quiet "-q" flag has been added for use by the news system.
89 3. The character chaining has been deleted and the program now uses
90 hashing. This improves the speed of the program, especially
91 during decompression. Other speed improvements have been made,
92 such as using putc() instead of fwrite().
94 4. A large table is used on large machines when a relatively small
95 number of bits is specified. This saves much time when compressing
96 for a 16-bit machine on a 32-bit virtual machine. Note that the
97 speed improvement only occurs when the input file is > 30000
98 characters, and the -b BITS is less than or equal to the cutoff
99 described below.
101 Most of these changes were made by James A. Woods (ames!jaw). Thank you
102 James!
104 To compile compress:
106 cc -O -DUSERMEM=usermem -o compress compress.c
108 Where "usermem" is the amount of physical user memory available (in bytes).
109 If any physical memory is to be reserved for other processes, put in
110 "-DSACREDMEM sacredmem", where "sacredmem" is the amount to be reserved.
112 The difference "usermem-sacredmem" determines the maximum BITS that can be
113 specified, and the cutoff bits where the large+fast table is used.
115 memory: at least BITS cutoff
116 ------ -- ----- ---- ------
117 4,718,592 16 13
118 2,621,440 16 12
119 1,572,864 16 11
120 1,048,576 16 10
121 631,808 16 --
122 329,728 15 --
123 178,176 14 --
124 99,328 13 --
125 0 12 --
127 The default memory size is 750,000 which gives a maximum BITS=16 and no
128 large+fast table.
130 The maximum bits can be overruled by specifying "-DBITS=bits" at
131 compilation time.
133 If your machine doesn't support unsigned characters, define "NO_UCHAR"
134 when compiling.
136 If your machine has "int" as 16-bits, define "SHORT_INT" when compiling.
138 After compilation, move "compress" to a standard executable location, such
139 as /usr/local. Then:
140 cd /usr/local
141 ln compress uncompress
142 ln compress zcat
144 On machines that have a fixed stack size (such as Perkin-Elmer), set the
145 stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer).
147 Next, install the manual (compress.l).
148 cp compress.l /usr/man/manl
149 cd /usr/man/manl
150 ln compress.l uncompress.l
151 ln compress.l zcat.l
153 - or -
155 cp compress.l /usr/man/man1/compress.1
156 cd /usr/man/man1
157 ln compress.1 uncompress.1
158 ln compress.1 zcat.1
160 regards,
161 petsd!joe
163 Here is a note from the net:
165 >From hplabs!pesnta!amd!turtlevax!ken Sat Jan 5 03:35:20 1985
166 Path: ames!hplabs!pesnta!amd!turtlevax!ken
167 From: ken@turtlevax.UUCP (Ken Turkowski)
168 Newsgroups: net.sources
169 Subject: Re: Compress release 3.0 : sample Makefile
170 Organization: CADLINC, Inc. @ Menlo Park, CA
172 In the compress 3.0 source recently posted to mod.sources, there is a
173 #define variable which can be set for optimum performance on a machine
174 with a large amount of memory. A program (usermem) to calculate the
175 useable amount of physical user memory is enclosed, as well as a sample
176 4.2bsd Vax Makefile for compress.
178 Here is the README file from the previous version of compress (2.0):
180 >Enclosed is compress.c version 2.0 with the following bugs fixed:
181 >
182 >1. The packed files produced by compress are different on different
183 > machines and dependent on the vax sysgen option.
184 > The bug was in the different byte/bit ordering on the
185 > various machines. This has been fixed.
186 >
187 > This version is NOT compatible with the original vax posting
188 > unless the '-DCOMPATIBLE' option is specified to the C
189 > compiler. The original posting has a bug which I fixed,
190 > causing incompatible files. I recommend you NOT to use this
191 > option unless you already have a lot of packed files from
192 > the original posting by thomas.
193 >2. The exit status is not well defined (on some machines) causing the
194 > scripts to fail.
195 > The exit status is now 0,1 or 2 and is documented in
196 > compress.l.
197 >3. The function getopt() is not available in all C libraries.
198 > The function getopt() is no longer referenced by the
199 > program.
200 >4. Error status is not being checked on the fwrite() and fflush() calls.
201 > Fixed.
202 >
203 >The following enhancements have been made:
204 >
205 >1. Added facilities of "compact" into the compress program. "Pack",
206 > "Unpack", and "Pcat" are no longer required (no longer supplied).
207 >2. Installed work around for C compiler bug with "-O".
208 >3. Added a magic number header (\037\235). Put the bits specified
209 > in the file.
210 >4. Added "-f" flag to force overwrite of output file.
211 >5. Added "-c" flag and "zcat" program. 'ln compress zcat' after you
212 > compile.
213 >6. The 'uncompress' script has been deleted; simply
214 > 'ln compress uncompress' after you compile and it will work.
215 >7. Removed extra bit masking for machines that support unsigned
216 > characters. If your machine doesn't support unsigned characters,
217 > define "NO_UCHAR" when compiling.
218 >
219 >Compile "compress.c" with "-O -o compress" flags. Move "compress" to a
220 >standard executable location, such as /usr/local. Then:
221 > cd /usr/local
222 > ln compress uncompress
223 > ln compress zcat
224 >
225 >On machines that have a fixed stack size (such as Perkin-Elmer), set the
226 >stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer).
227 >
228 >Next, install the manual (compress.l).
229 > cp compress.l /usr/man/manl - or -
230 > cp compress.l /usr/man/man1/compress.1
231 >
232 >Here is the README that I sent with my first posting:
233 >
234 >>Enclosed is a modified version of compress.c, along with scripts to make it
235 >>run identically to pack(1), unpack(1), an pcat(1). Here is what I
236 >>(petsd!joe) and a colleague (petsd!peora!srd) did:
237 >>
238 >>1. Removed VAX dependencies.
239 >>2. Changed the struct to separate arrays; saves mucho memory.
240 >>3. Did comparisons in unsigned, where possible. (Faster on Perkin-Elmer.)
241 >>4. Sorted the character next chain and changed the search to stop
242 >>prematurely. This saves a lot on the execution time when compressing.
243 >>
244 >>This version is totally compatible with the original version. Even though
245 >>lint(1) -p has no complaints about compress.c, it won't run on a 16-bit
246 >>machine, due to the size of the arrays.
247 >>
248 >>Here is the README file from the original author:
249 >>
250 >>>Well, with all this discussion about file compression (for news batching
251 >>>in particular) going around, I decided to implement the text compression
252 >>>algorithm described in the June Computer magazine. The author claimed
253 >>>blinding speed and good compression ratios. It's certainly faster than
254 >>>compact (but, then, what wouldn't be), but it's also the same speed as
255 >>>pack, and gets better compression than both of them. On 350K bytes of
256 >>>unix-wizards, compact took about 8 minutes of CPU, pack took about 80
257 >>>seconds, and compress (herein) also took 80 seconds. But, compact and
258 >>>pack got about 30% compression, whereas compress got over 50%. So, I
259 >>>decided I had something, and that others might be interested, too.
260 >>>
261 >>>As is probably true of compact and pack (although I haven't checked),
262 >>>the byte order within a word is probably relevant here, but as long as
263 >>>you stay on a single machine type, you should be ok. (Can anybody
264 >>>elucidate on this?) There are a couple of asm's in the code (extv and
265 >>>insv instructions), so anyone porting it to another machine will have to
266 >>>deal with this anyway (and could probably make it compatible with Vax
267 >>>byte order at the same time). Anyway, I've linted the code (both with
268 >>>and without -p), so it should run elsewhere. Note the longs in the
269 >>>code, you can take these out if you reduce BITS to <= 15.
270 >>>
271 >>>Have fun, and as always, if you make good enhancements, or bug fixes,
272 >>>I'd like to see them.
273 >>>
274 >>>=Spencer (thomas@utah-20, {harpo,hplabs,arizona}!utah-cs!thomas)
275 >>
276 >> regards,
277 >> joe
278 >>
279 >>--
280 >>Full-Name: Joseph M. Orost
281 >>UUCP: ..!{decvax,ucbvax,ihnp4}!vax135!petsd!joe
282 >>US Mail: MS 313; Perkin-Elmer; 106 Apple St; Tinton Falls, NJ 07724
283 >>Phone: (201) 870-5844