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Subject: Re: Compression, was Question about Bit storage.

Author: Dan Andersson

Date: 17:54:25 01/30/02

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>That would be 4 bits.  Does that mean that the shrinkage is 2^4th = 16 fold?  A
>simple way to accomplish that is to have 16 separate tables.  Then you don't
>need any bits for castling rights.
The number of bits depend on how efficient the encoding is. Castling information
is implicit in the majority of cases. i.e. the king is off the castling square.
When calculating compression efficiency one takes into account the size of the
program. And that includes data also. For example:
  You could have a compression that compresses Moby Dick to one bit. A one. And
all other cases a zero followed by other any other text (or text compressed by a
predetermined algorithm). But the size of that program would contain a
representation of Moby Dick. Thus not gaining any real benefit from it because
every other text will have an extra bit.
  So the gain of separate coding of special cases comes into play only when
additional symmetries and recursive structures appear.
  I do however think the idea of goal oriented sparse tables are good. As the
sliding piece idea from Lez. It is similar but simpler and more effective than
my idea of a sparse table containing enough position for search to find a match.
Even though they may need more than the optimal number of moves to win. One
complication remains, it is neccessary to ensure that the 50-move rule is not
breached.

MvH Dan Andersson



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