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Subject: Re: Compression idea (8:1 for pawnless endgame tablebase files)

Author: Ernst A. Heinz

Date: 14:37:56 02/10/01

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Hi Dann,

>Les Fernandez had an interesting compression idea that might be useful for
>database files.  There is some VB code and an explanation here for an idea to
>reduce the size of endgame tablebase files:
>
>ftp://cap.connx.com/pub/VbRotations/
>
>It would be interesting to get some feedback on this idea.  Will it provide the
>desired compression?  If it could pack the data by a factor of 8, it would be
>helpful for I/O speed and other benefits of that nature.
>
>Perhaps it is possible to get even greater compression levels.

Rotational symmetries have been used in compressing the _index
ranges_ of endgame databases since the 1980s at least. Ken
Thompson's databases already incorporated this as a key feature.

Two survey articles about the topic of efficient index schemes
for endgame databases have recently been published in the
ICCA/ICGA Journal.

 * E.V. Nalimov, G.McC. Haworth, and E.A. Heinz.
   ``Space-efficient indexing of chess endgame tables.''
   ICGA Journal, Vol. 23, No. 3, pages 148-162, September 2000.

 * E.A. Heinz.
   ``Endgame databases and efficient index schemes.''
   ICCA Journal, Vol. 22, No. 1, pages 22-32, March 1999.

An electronic preprint of the latter is available for download
on my WWW pages at http://supertech.lcs.mit.edu/~heinz/.

=Ernst=



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