[Gnu-arch-users] Re: [ANNOUNCEMENT] /Arch/ embraces `git'

[Szilard Hajba]

On Wed, Apr 20, 2005 at 02:32:29PM -0700, Tom Lord wrote:
> My understanding is still superficial in that detail:  I gather that
> zip formats are standardized by a IETF document.  I am not certain
> that the spec implies deterministic output.   I am not certain that
> the way I'm driving `libz', so as to be compatible with Linus' code,
> is the right way to do it.

Hi!

Some compressions are really standardized, but this doesn't guarantees that
the compressed files are the same. The standards define some methods for
uncompressing, but does not define how to get the compressed form.

Let's define a 'standard' compressed format like this:

{<character>,<repeat>}*

This character sequence:   "aaaaaabbbbbccccccdddddddddddddddddddd"
Can be written as compressed: "{a,6}{b,5}{c,6}{d,20}"

But the following string is also suitable:
Can be written as compressed: "{a,6}{b,5}{c,6}{d,5}{d,5}{d,5}{d,5}"

Tha standard defines a format and the uncompression methods. But the way I gat
to the compressed file is not defined. Compression programs are evoluting
slowly, the generated output is better and better, but the underling standard,
the file format is the same.

Of course it is possible to make such a compression standard that defines
exact compressed data, but then further developments are disabled, so it is
not a good thing.

$zilu

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Szilard Hajba                   Symbion Ltd.
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