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

[Goswin Brederlow <goswin.brederlow@student.uni-tuebingen.de>]

>>>>> " " == Otto Wyss <otto.wyss@bluewin.ch> writes:

    >> > 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.

Yes THEY are. Most of the time each character is encoded by its own
table, which is constrcted out of all the characters encoded or
decoded before. The tables are static but 100% dependent on the
data. Change one char and all later tables change. (except when gzip
cleans the dictionary, see other mail).

MfG
        Goswin