Mail Archives: djgpp/2009/05/26/02:45:11

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From: Rugxulo <rugxulo AT gmail DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Gzip 1.2.4 "-9" hack (improved compression) / Unzip 6.0
Date: Mon, 25 May 2009 23:38:04 -0700 (PDT)
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

The ultimate .gz compressor is probably 7-Zip / p7zip, but it's very
very slow. But if you want better compression without the huge speed
penalty, you can compile Gzip 1.2.4 (only) with Ilia Muraviev's "-9"
hack (two-byte lookahead or whatever). As he calls it, it's a five-
minute hack, so it's not ported to 1.3.12 or Zlib. But hey, it
improves the compression while still keeping older levels for fastest
speed ratio. So, if you want a bit better speed, try his modified
DEFLATE.C (and use -DNO_ASM and remove all mentions of match.S from
the makefile, and fix the silly tab error, and it should compile and
work correctly). And yes, it's 100% compatible output.

Basically, it compresses better than typical Gzip "-9" but somewhat

                                         enwik8          enwik9
gzip124hack           -9    36,273,716       321,050,648
gzip 1.3.5               -9    36,445,248       322,591,995  (original patched
DEFLATE.C and Win32 binary)        (311k, includes
everything necessary, mainly full sources + patch + OpenWatcom DOS +
Win32 compiles, this was before I knew why DJGPP wasn't byte
identical, don't forget -DNO_ASM and don't use match.S !!!)

P.S. Since I'm talking about compression, Info-Zip 6.0 was *finally*
released last month (and Zip 3.0 last year and 3.1b beta srcs
recently), default package includes MSC 16-bit and  :-)  DJGPPv2  :-)
32-bit .EXEs (with Bzip2 method support). Not sure why no default
binaries for Zip 3.0, I did compile for them (minor bug on DR-DOS, MS-
DOS 6.22 re: "-f", probably still unresolved, bah), but anyways, it's
easy to build.

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