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Subject: Re: Hashing pawn structures - how?

Author: Robert Hyatt

Date: 07:31:35 10/31/98

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On October 30, 1998 at 14:16:28, Peter Kasinski wrote:

>I guess the usual position+score is of little value here. I need square-level
>details for subsequent piece evaluation. Somehow storing an array of squares
>with each hash entry doesn't look appealing.
>Does this information get hashed as well? Should I have a hash signature for,
>say, an outpost on each square? And if so, how is it possible to update
>hash_code incrementally?
>
>Thank you very much, as always.
>PK.

easy...  create a "pawn structure hash 'structure'"... in it you put the
normal hash signature (only using the locations of pawns, of course), plus
the output of your pawn evaluation (you have to be very careful and *not*
include *anything* that has to do with pieces at this point).  Plus you
add any things that your pawn eval sets and passes to successive evaluation
routines...  ie a map of weak pawns, number of isolated pawns on open files,
a map of which pawns are passed, etc.  Then the hash "hit" can produce
*everything* a call to your pawn structure evaluator normally would...  only
far faster...

Just don't forget that the hash signature depends only on pawns, so the stuff
you compute there should depend only on pawns...  you can add a second pawn
evaluator (I did in crafty) if you have some analysis that depends on where
pieces are or how many there are...



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