/usr.bin/compress/doc/README
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1 2 @(#)README 8.1 (Berkeley) 6/9/93 3 $FreeBSD$ 4 5Compress version 4.0 improvements over 3.0: 6 o compress() speedup (10-50%) by changing division hash to xor 7 o decompress() speedup (5-10%) 8 o Memory requirements reduced (3-30%) 9 o Stack requirements reduced to less than 4kb 10 o Removed 'Big+Fast' compress code (FBITS) because of compress speedup 11 o Portability mods for Z8000 and PC/XT (but not zeus 3.2) 12 o Default to 'quiet' mode 13 o Unification of 'force' flags 14 o Manual page overhaul 15 o Portability enhancement for M_XENIX 16 o Removed text on #else and #endif 17 o Added "-V" switch to print version and options 18 o Added #defines for SIGNED_COMPARE_SLOW 19 o Added Makefile and "usermem" program 20 o Removed all floating point computations 21 o New programs: [deleted] 22 23The "usermem" script attempts to determine the maximum process size. Some 24editing of the script may be necessary (see the comments). [It should work 25fine on 4.3 BSD.] If you can't get it to work at all, just create file 26"USERMEM" containing the maximum process size in decimal. 27 28The following preprocessor symbols control the compilation of "compress.c": 29 30 o USERMEM Maximum process memory on the system 31 o SACREDMEM Amount to reserve for other processes 32 o SIGNED_COMPARE_SLOW Unsigned compare instructions are faster 33 o NO_UCHAR Don't use "unsigned char" types 34 o BITS Overrules default set by USERMEM-SACREDMEM 35 o vax Generate inline assembler 36 o interdata Defines SIGNED_COMPARE_SLOW 37 o M_XENIX Makes arrays < 65536 bytes each 38 o pdp11 BITS=12, NO_UCHAR 39 o z8000 BITS=12 40 o pcxt BITS=12 41 o BSD4_2 Allow long filenames ( > 14 characters) & 42 Call setlinebuf(stderr) 43 44The difference "usermem-sacredmem" determines the maximum BITS that can be 45specified with the "-b" flag. 46 47memory: at least BITS 48------ -- ----- ---- 49 433,484 16 50 229,600 15 51 127,536 14 52 73,464 13 53 0 12 54 55The default is BITS=16. 56 57The maximum bits can be overruled by specifying "-DBITS=bits" at 58compilation time. 59 60WARNING: files compressed on a large machine with more bits than allowed by 61a version of compress on a smaller machine cannot be decompressed! Use the 62"-b12" flag to generate a file on a large machine that can be uncompressed 63on a 16-bit machine. 64 65The output of compress 4.0 is fully compatible with that of compress 3.0. 66In other words, the output of compress 4.0 may be fed into uncompress 3.0 or 67the output of compress 3.0 may be fed into uncompress 4.0. 68 69The output of compress 4.0 not compatible with that of 70compress 2.0. However, compress 4.0 still accepts the output of 71compress 2.0. To generate output that is compatible with compress 722.0, use the undocumented "-C" flag. 73 74 -from mod.sources, submitted by vax135!petsd!joe (Joe Orost), 8/1/85 75-------------------------------- 76 77Enclosed is compress version 3.0 with the following changes: 78 791. "Block" compression is performed. After the BITS run out, the 80 compression ratio is checked every so often. If it is decreasing, 81 the table is cleared and a new set of substrings are generated. 82 83 This makes the output of compress 3.0 not compatible with that of 84 compress 2.0. However, compress 3.0 still accepts the output of 85 compress 2.0. To generate output that is compatible with compress 86 2.0, use the undocumented "-C" flag. 87 882. A quiet "-q" flag has been added for use by the news system. 89 903. The character chaining has been deleted and the program now uses 91 hashing. This improves the speed of the program, especially 92 during decompression. Other speed improvements have been made, 93 such as using putc() instead of fwrite(). 94 954. A large table is used on large machines when a relatively small 96 number of bits is specified. This saves much time when compressing 97 for a 16-bit machine on a 32-bit virtual machine. Note that the 98 speed improvement only occurs when the input file is > 30000 99 characters, and the -b BITS is less than or equal to the cutoff 100 described below. 101 102Most of these changes were made by James A. Woods (ames!jaw). Thank you 103James! 104 105To compile compress: 106 107 cc -O -DUSERMEM=usermem -o compress compress.c 108 109Where "usermem" is the amount of physical user memory available (in bytes). 110If any physical memory is to be reserved for other processes, put in 111"-DSACREDMEM sacredmem", where "sacredmem" is the amount to be reserved. 112 113The difference "usermem-sacredmem" determines the maximum BITS that can be 114specified, and the cutoff bits where the large+fast table is used. 115 116memory: at least BITS cutoff 117------ -- ----- ---- ------ 118 4,718,592 16 13 119 2,621,440 16 12 120 1,572,864 16 11 121 1,048,576 16 10 122 631,808 16 -- 123 329,728 15 -- 124 178,176 14 -- 125 99,328 13 -- 126 0 12 -- 127 128The default memory size is 750,000 which gives a maximum BITS=16 and no 129large+fast table. 130 131The maximum bits can be overruled by specifying "-DBITS=bits" at 132compilation time. 133 134If your machine doesn't support unsigned characters, define "NO_UCHAR" 135when compiling. 136 137If your machine has "int" as 16-bits, define "SHORT_INT" when compiling. 138 139After compilation, move "compress" to a standard executable location, such 140as /usr/local. Then: 141 cd /usr/local 142 ln compress uncompress 143 ln compress zcat 144 145On machines that have a fixed stack size (such as Perkin-Elmer), set the 146stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer). 147 148Next, install the manual (compress.l). 149 cp compress.l /usr/man/manl 150 cd /usr/man/manl 151 ln compress.l uncompress.l 152 ln compress.l zcat.l 153 154 - or - 155 156 cp compress.l /usr/man/man1/compress.1 157 cd /usr/man/man1 158 ln compress.1 uncompress.1 159 ln compress.1 zcat.1 160 161 regards, 162 petsd!joe 163 164Here is a note from the net: 165 166>From hplabs!pesnta!amd!turtlevax!ken Sat Jan 5 03:35:20 1985 167Path: ames!hplabs!pesnta!amd!turtlevax!ken 168From: ken@turtlevax.UUCP (Ken Turkowski) 169Newsgroups: net.sources 170Subject: Re: Compress release 3.0 : sample Makefile 171Organization: CADLINC, Inc. @ Menlo Park, CA 172 173In the compress 3.0 source recently posted to mod.sources, there is a 174#define variable which can be set for optimum performance on a machine 175with a large amount of memory. A program (usermem) to calculate the 176usable amount of physical user memory is enclosed, as well as a sample 1774.2BSD Vax Makefile for compress. 178 179Here is the README file from the previous version of compress (2.0): 180 181>Enclosed is compress.c version 2.0 with the following bugs fixed: 182> 183>1. The packed files produced by compress are different on different 184> machines and dependent on the vax sysgen option. 185> The bug was in the different byte/bit ordering on the 186> various machines. This has been fixed. 187> 188> This version is NOT compatible with the original vax posting 189> unless the '-DCOMPATIBLE' option is specified to the C 190> compiler. The original posting has a bug which I fixed, 191> causing incompatible files. I recommend you NOT to use this 192> option unless you already have a lot of packed files from 193> the original posting by Thomas. 194>2. The exit status is not well defined (on some machines) causing the 195> scripts to fail. 196> The exit status is now 0,1 or 2 and is documented in 197> compress.l. 198>3. The function getopt() is not available in all C libraries. 199> The function getopt() is no longer referenced by the 200> program. 201>4. Error status is not being checked on the fwrite() and fflush() calls. 202> Fixed. 203> 204>The following enhancements have been made: 205> 206>1. Added facilities of "compact" into the compress program. "Pack", 207> "Unpack", and "Pcat" are no longer required (no longer supplied). 208>2. Installed work around for C compiler bug with "-O". 209>3. Added a magic number header (\037\235). Put the bits specified 210> in the file. 211>4. Added "-f" flag to force overwrite of output file. 212>5. Added "-c" flag and "zcat" program. 'ln compress zcat' after you 213> compile. 214>6. The 'uncompress' script has been deleted; simply 215> 'ln compress uncompress' after you compile and it will work. 216>7. Removed extra bit masking for machines that support unsigned 217> characters. If your machine doesn't support unsigned characters, 218> define "NO_UCHAR" when compiling. 219> 220>Compile "compress.c" with "-O -o compress" flags. Move "compress" to a 221>standard executable location, such as /usr/local. Then: 222> cd /usr/local 223> ln compress uncompress 224> ln compress zcat 225> 226>On machines that have a fixed stack size (such as Perkin-Elmer), set the 227>stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer). 228> 229>Next, install the manual (compress.l). 230> cp compress.l /usr/man/manl - or - 231> cp compress.l /usr/man/man1/compress.1 232> 233>Here is the README that I sent with my first posting: 234> 235>>Enclosed is a modified version of compress.c, along with scripts to make it 236>>run identically to pack(1), unpack(1), and pcat(1). Here is what I 237>>(petsd!joe) and a colleague (petsd!peora!srd) did: 238>> 239>>1. Removed VAX dependencies. 240>>2. Changed the struct to separate arrays; saves mucho memory. 241>>3. Did comparisons in unsigned, where possible. (Faster on Perkin-Elmer.) 242>>4. Sorted the character next chain and changed the search to stop 243>>prematurely. This saves a lot on the execution time when compressing. 244>> 245>>This version is totally compatible with the original version. Even though 246>>lint(1) -p has no complaints about compress.c, it won't run on a 16-bit 247>>machine, due to the size of the arrays. 248>> 249>>Here is the README file from the original author: 250>> 251>>>Well, with all this discussion about file compression (for news batching 252>>>in particular) going around, I decided to implement the text compression 253>>>algorithm described in the June Computer magazine. The author claimed 254>>>blinding speed and good compression ratios. It's certainly faster than 255>>>compact (but, then, what wouldn't be), but it's also the same speed as 256>>>pack, and gets better compression than both of them. On 350K bytes of 257>>>Unix-wizards, compact took about 8 minutes of CPU, pack took about 80 258>>>seconds, and compress (herein) also took 80 seconds. But, compact and 259>>>pack got about 30% compression, whereas compress got over 50%. So, I 260>>>decided I had something, and that others might be interested, too. 261>>> 262>>>As is probably true of compact and pack (although I haven't checked), 263>>>the byte order within a word is probably relevant here, but as long as 264>>>you stay on a single machine type, you should be ok. (Can anybody 265>>>elucidate on this?) There are a couple of asm's in the code (extv and 266>>>insv instructions), so anyone porting it to another machine will have to 267>>>deal with this anyway (and could probably make it compatible with Vax 268>>>byte order at the same time). Anyway, I've linted the code (both with 269>>>and without -p), so it should run elsewhere. Note the longs in the 270>>>code, you can take these out if you reduce BITS to <= 15. 271>>> 272>>>Have fun, and as always, if you make good enhancements, or bug fixes, 273>>>I'd like to see them. 274>>> 275>>>=Spencer (thomas@utah-20, {harpo,hplabs,arizona}!utah-cs!thomas) 276>> 277>> regards, 278>> joe 279>> 280>>-- 281>>Full-Name: Joseph M. Orost 282>>UUCP: ..!{decvax,ucbvax,ihnp4}!vax135!petsd!joe 283>>US Mail: MS 313; Perkin-Elmer; 106 Apple St; Tinton Falls, NJ 07724 284>>Phone: (201) 870-5844