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285 lines
11 KiB
Plaintext
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@(#)README 8.1 (Berkeley) 6/9/93
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$FreeBSD$
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Compress version 4.0 improvements over 3.0:
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o compress() speedup (10-50%) by changing division hash to xor
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o decompress() speedup (5-10%)
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o Memory requirements reduced (3-30%)
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o Stack requirements reduced to less than 4kb
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o Removed 'Big+Fast' compress code (FBITS) because of compress speedup
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o Portability mods for Z8000 and PC/XT (but not zeus 3.2)
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o Default to 'quiet' mode
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o Unification of 'force' flags
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o Manual page overhaul
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o Portability enhancement for M_XENIX
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o Removed text on #else and #endif
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o Added "-V" switch to print version and options
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o Added #defines for SIGNED_COMPARE_SLOW
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o Added Makefile and "usermem" program
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o Removed all floating point computations
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o New programs: [deleted]
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The "usermem" script attempts to determine the maximum process size. Some
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editing of the script may be necessary (see the comments). [It should work
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fine on 4.3 BSD.] If you can't get it to work at all, just create file
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"USERMEM" containing the maximum process size in decimal.
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The following preprocessor symbols control the compilation of "compress.c":
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o USERMEM Maximum process memory on the system
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o SACREDMEM Amount to reserve for other processes
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o SIGNED_COMPARE_SLOW Unsigned compare instructions are faster
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o NO_UCHAR Don't use "unsigned char" types
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o BITS Overrules default set by USERMEM-SACREDMEM
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o vax Generate inline assembler
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o interdata Defines SIGNED_COMPARE_SLOW
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o M_XENIX Makes arrays < 65536 bytes each
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o pdp11 BITS=12, NO_UCHAR
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o z8000 BITS=12
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o pcxt BITS=12
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o BSD4_2 Allow long filenames ( > 14 characters) &
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Call setlinebuf(stderr)
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The difference "usermem-sacredmem" determines the maximum BITS that can be
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specified with the "-b" flag.
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memory: at least BITS
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------ -- ----- ----
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433,484 16
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229,600 15
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127,536 14
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73,464 13
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0 12
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The default is BITS=16.
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The maximum bits can be overruled by specifying "-DBITS=bits" at
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compilation time.
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WARNING: files compressed on a large machine with more bits than allowed by
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a version of compress on a smaller machine cannot be decompressed! Use the
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"-b12" flag to generate a file on a large machine that can be uncompressed
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on a 16-bit machine.
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The output of compress 4.0 is fully compatible with that of compress 3.0.
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In other words, the output of compress 4.0 may be fed into uncompress 3.0 or
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the output of compress 3.0 may be fed into uncompress 4.0.
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The output of compress 4.0 not compatible with that of
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compress 2.0. However, compress 4.0 still accepts the output of
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compress 2.0. To generate output that is compatible with compress
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2.0, use the undocumented "-C" flag.
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-from mod.sources, submitted by vax135!petsd!joe (Joe Orost), 8/1/85
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--------------------------------
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Enclosed is compress version 3.0 with the following changes:
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1. "Block" compression is performed. After the BITS run out, the
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compression ratio is checked every so often. If it is decreasing,
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the table is cleared and a new set of substrings are generated.
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This makes the output of compress 3.0 not compatible with that of
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compress 2.0. However, compress 3.0 still accepts the output of
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compress 2.0. To generate output that is compatible with compress
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2.0, use the undocumented "-C" flag.
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2. A quiet "-q" flag has been added for use by the news system.
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3. The character chaining has been deleted and the program now uses
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hashing. This improves the speed of the program, especially
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during decompression. Other speed improvements have been made,
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such as using putc() instead of fwrite().
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4. A large table is used on large machines when a relatively small
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number of bits is specified. This saves much time when compressing
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for a 16-bit machine on a 32-bit virtual machine. Note that the
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speed improvement only occurs when the input file is > 30000
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characters, and the -b BITS is less than or equal to the cutoff
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described below.
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Most of these changes were made by James A. Woods (ames!jaw). Thank you
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James!
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To compile compress:
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cc -O -DUSERMEM=usermem -o compress compress.c
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Where "usermem" is the amount of physical user memory available (in bytes).
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If any physical memory is to be reserved for other processes, put in
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"-DSACREDMEM sacredmem", where "sacredmem" is the amount to be reserved.
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The difference "usermem-sacredmem" determines the maximum BITS that can be
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specified, and the cutoff bits where the large+fast table is used.
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memory: at least BITS cutoff
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------ -- ----- ---- ------
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4,718,592 16 13
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2,621,440 16 12
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1,572,864 16 11
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1,048,576 16 10
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631,808 16 --
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329,728 15 --
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178,176 14 --
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99,328 13 --
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0 12 --
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The default memory size is 750,000 which gives a maximum BITS=16 and no
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large+fast table.
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The maximum bits can be overruled by specifying "-DBITS=bits" at
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compilation time.
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If your machine doesn't support unsigned characters, define "NO_UCHAR"
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when compiling.
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If your machine has "int" as 16-bits, define "SHORT_INT" when compiling.
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After compilation, move "compress" to a standard executable location, such
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as /usr/local. Then:
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cd /usr/local
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ln compress uncompress
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ln compress zcat
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On machines that have a fixed stack size (such as Perkin-Elmer), set the
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stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer).
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Next, install the manual (compress.l).
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cp compress.l /usr/man/manl
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cd /usr/man/manl
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ln compress.l uncompress.l
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ln compress.l zcat.l
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- or -
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cp compress.l /usr/man/man1/compress.1
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cd /usr/man/man1
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ln compress.1 uncompress.1
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ln compress.1 zcat.1
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regards,
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petsd!joe
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Here is a note from the net:
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>From hplabs!pesnta!amd!turtlevax!ken Sat Jan 5 03:35:20 1985
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Path: ames!hplabs!pesnta!amd!turtlevax!ken
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From: ken@turtlevax.UUCP (Ken Turkowski)
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Newsgroups: net.sources
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Subject: Re: Compress release 3.0 : sample Makefile
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Organization: CADLINC, Inc. @ Menlo Park, CA
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In the compress 3.0 source recently posted to mod.sources, there is a
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#define variable which can be set for optimum performance on a machine
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with a large amount of memory. A program (usermem) to calculate the
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usable amount of physical user memory is enclosed, as well as a sample
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4.2BSD Vax Makefile for compress.
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Here is the README file from the previous version of compress (2.0):
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>Enclosed is compress.c version 2.0 with the following bugs fixed:
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>
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>1. The packed files produced by compress are different on different
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> machines and dependent on the vax sysgen option.
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> The bug was in the different byte/bit ordering on the
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> various machines. This has been fixed.
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>
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> This version is NOT compatible with the original vax posting
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> unless the '-DCOMPATIBLE' option is specified to the C
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> compiler. The original posting has a bug which I fixed,
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> causing incompatible files. I recommend you NOT to use this
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> option unless you already have a lot of packed files from
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> the original posting by Thomas.
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>2. The exit status is not well defined (on some machines) causing the
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> scripts to fail.
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> The exit status is now 0,1 or 2 and is documented in
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> compress.l.
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>3. The function getopt() is not available in all C libraries.
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> The function getopt() is no longer referenced by the
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> program.
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>4. Error status is not being checked on the fwrite() and fflush() calls.
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> Fixed.
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>
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>The following enhancements have been made:
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>
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>1. Added facilities of "compact" into the compress program. "Pack",
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> "Unpack", and "Pcat" are no longer required (no longer supplied).
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>2. Installed work around for C compiler bug with "-O".
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>3. Added a magic number header (\037\235). Put the bits specified
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> in the file.
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>4. Added "-f" flag to force overwrite of output file.
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>5. Added "-c" flag and "zcat" program. 'ln compress zcat' after you
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> compile.
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>6. The 'uncompress' script has been deleted; simply
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> 'ln compress uncompress' after you compile and it will work.
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>7. Removed extra bit masking for machines that support unsigned
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> characters. If your machine doesn't support unsigned characters,
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> define "NO_UCHAR" when compiling.
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>
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>Compile "compress.c" with "-O -o compress" flags. Move "compress" to a
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>standard executable location, such as /usr/local. Then:
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> cd /usr/local
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> ln compress uncompress
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> ln compress zcat
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>
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>On machines that have a fixed stack size (such as Perkin-Elmer), set the
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>stack to at least 12kb. ("setstack compress 12" on Perkin-Elmer).
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>
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>Next, install the manual (compress.l).
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> cp compress.l /usr/man/manl - or -
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> cp compress.l /usr/man/man1/compress.1
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>
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>Here is the README that I sent with my first posting:
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>
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>>Enclosed is a modified version of compress.c, along with scripts to make it
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>>run identically to pack(1), unpack(1), and pcat(1). Here is what I
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>>(petsd!joe) and a colleague (petsd!peora!srd) did:
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>>
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>>1. Removed VAX dependencies.
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>>2. Changed the struct to separate arrays; saves mucho memory.
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>>3. Did comparisons in unsigned, where possible. (Faster on Perkin-Elmer.)
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>>4. Sorted the character next chain and changed the search to stop
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>>prematurely. This saves a lot on the execution time when compressing.
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>>
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>>This version is totally compatible with the original version. Even though
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>>lint(1) -p has no complaints about compress.c, it won't run on a 16-bit
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>>machine, due to the size of the arrays.
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>>
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>>Here is the README file from the original author:
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>>
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>>>Well, with all this discussion about file compression (for news batching
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>>>in particular) going around, I decided to implement the text compression
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>>>algorithm described in the June Computer magazine. The author claimed
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>>>blinding speed and good compression ratios. It's certainly faster than
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>>>compact (but, then, what wouldn't be), but it's also the same speed as
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>>>pack, and gets better compression than both of them. On 350K bytes of
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>>>Unix-wizards, compact took about 8 minutes of CPU, pack took about 80
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>>>seconds, and compress (herein) also took 80 seconds. But, compact and
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>>>pack got about 30% compression, whereas compress got over 50%. So, I
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>>>decided I had something, and that others might be interested, too.
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>>>
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>>>As is probably true of compact and pack (although I haven't checked),
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>>>the byte order within a word is probably relevant here, but as long as
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>>>you stay on a single machine type, you should be ok. (Can anybody
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>>>elucidate on this?) There are a couple of asm's in the code (extv and
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>>>insv instructions), so anyone porting it to another machine will have to
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>>>deal with this anyway (and could probably make it compatible with Vax
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>>>byte order at the same time). Anyway, I've linted the code (both with
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>>>and without -p), so it should run elsewhere. Note the longs in the
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>>>code, you can take these out if you reduce BITS to <= 15.
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>>>
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>>>Have fun, and as always, if you make good enhancements, or bug fixes,
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>>>I'd like to see them.
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>>>
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>>>=Spencer (thomas@utah-20, {harpo,hplabs,arizona}!utah-cs!thomas)
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>>
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>> regards,
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>> joe
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>>
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>>--
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>>Full-Name: Joseph M. Orost
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>>UUCP: ..!{decvax,ucbvax,ihnp4}!vax135!petsd!joe
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>>US Mail: MS 313; Perkin-Elmer; 106 Apple St; Tinton Falls, NJ 07724
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>>Phone: (201) 870-5844
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