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Re: Solving the compression dilema when rsync-ing Debian versions

> >         gzip --compress-like=old-foo foo
> > 
> > where foo will be compressed as old-foo was or as aquivalent as
> > possible. Gzip does not need to know anything about foo except how it
> > was compressed. The switch "--compress-like" could be added to any
> > compression algorithmus (bzip?) as long as it's easy to retrieve the
> No, this won't work with very many compression algorithms.  Most
> algorithms update their dictionaries/probability tables dynamically based
> on input.  There isn't just one static table that could be used for
> another file, since the table is automatically updated after every (or
> near every) transmitted or decoded symbol.  Further, the algorithms start
> with blank tables on both ends (compression and decompression), the
> algorithm doesn't transmit the tables (which can be quite large for higher
> order statistical models).
Well the table is perfectly static when the compression ends. Even if
the table isn't transmitted itself, its information is contained in the
compressed file, otherwise the file couldn't be decompressed either. 

O. Wyss

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