Re: Fixpoint for LZH

From: David Bernier (david250_at_videotron.ca)
Date: 07/19/04 

Date: Mon, 19 Jul 2004 06:04:19 -0400

Dik T. Winter wrote:
> In article <1090049632.322988@athnrd02.forthnet.gr> morpheus@olympus.mons writes:
[...]

> >
> > It is possible that several schemes may have a fixed point, but it
> > appears to me as though a filesize change doesn't imply anything about
> > the existence of said point.
>
> Where do I say that there is an implication? I only say that it is
> possible that such does exist!
>
> > In that sense, zip appears to be fundamentally different from Stuffit
> > for example, in that Stuffit for Macs if memory serves right, never
> > increased file size. It's been a while since I was using a Mac, so my
> > memory may be failing me on this.
>
> Stuffit will never increase filesize indeed. But that is a program that
> uses quite a few different compression formats and if any of them fail
> to make the file shorter, it will just produce the original. The point
> was *not* whether a particular program has a fixed point (I know some
> for Stuffit), but whether a compression scheme has a fixed point.

I did a bit of experimentation with WinZip.

Starting with an uncompressed file, I used
WinZip (R) 9.0 in normal compression mode
to compress the original file up to
4 iterations.

The resulting file sizes appear below:

152,369,152 bytes // file f
  24,955,547 bytes // winzip(f)
  24,955,655 bytes // winzip^2(f)
  24,955,763 bytes // winzip^3(f)
  24,955,871 bytes // winzip^4(f)

David Bernier

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