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Subject: Re: How to use hashtable for bishops?

Author: Carmelo Calzerano

Date: 01:41:02 12/10/01

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On December 09, 2001 at 18:56:05, Pham Minh Tri wrote:

>On December 09, 2001 at 18:04:59, Matthias Gemuh wrote:
>
>>On December 09, 2001 at 17:55:43, Pham Minh Tri wrote:
>>
>>>On December 09, 2001 at 10:37:30, Robert Hyatt wrote:
>>>
>>>>On December 09, 2001 at 06:21:37, Pham Minh Tri wrote:
>>>>
>>>>>Someone told me that he used hashtable for bishops, but I do not understand how
>>>>>to do (unlike pawns, I found there was too little information to save for
>>>>>hashtable). Could someone explain to me or show me where to download the source
>>>>>code. Many thanks in advance.
>>>>
>>>>
>>>>You could, in theory, use special purpose hash tables for any evaluation
>>>>component that is costly to compute.  The danger is that this can become
>>>>very memory-intensive...
>>>
>>>Yes, but how? :)
>>
>>
>>Score batteries, pins, discovered checks, good/bad bishops, pairs, etc. :).
>
>Thanks, I undertand more. But could you explain more about pins and discovered
>checks? I think those factors concerns to many other pieces, not only bishops,
>so how to separate, compute and store them in hashtalbe?

Exactly: to get a reasonable bishop scoring, you should include in the hash
signature almost all other pieces (and pawns too, since good/bad bishops and
mobility basically depends on pawns position).
I know, this way you'll end up with the same signature you use in main hash
table, but well, I guess that's why nodody here uses bishop hashtables,
AFAIK... ;-)

>An other question: I know the mobility of bishop is expensive to compute, but I
>don't know how to save it in hashtable. Could anyone shed more light on this?

I don't think it is worth the trouble, but maybe a reasonable way would be
to consider the bishop's mobility as depending only upon pawns position, thus
using the pawns and the bishop (the bishop being scored only, not other bishops
of course) positions to get the hash signature.

Bye,
Carmelo




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