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Subject: Re: Question for Hyatt about Alpha/Beta

Author: Tord Romstad

Date: 06:54:55 02/06/04

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On February 06, 2004 at 09:08:28, Anthony Cozzie wrote:

>On February 06, 2004 at 07:22:19, Tord Romstad wrote:
>
>>It is much more expensive than that.  Remember that all squares are not
>>equally important, and that the bishop cannot safely move to all the squares
>>you attack.  For each square the bishop attacks, you must see if it can
>>move there without getting captured, and consider how useful it is to be
>>able to move to this square.  For each friendly pawn which obstructs the
>>bishop, you must consider how easy it is to advance this pawn.  Most of
>>this is quite expensive to compute, and I have been forced to do some
>>dubious shortcuts and approximations in order not to slow my engine down
>>too much.  Some day I should probably have a look at how Bob does this,
>>and see if there are some ideas there which I could use.
>>
>
>
>With rotated bitboards it is practically free; it is just a popcount8.
>
>Basically just popcount your index.

I don't see how you can do this with just a popcount.  First of all, how
do you get a bitboard containing all the squares the bishop can *safely*
reach?  Assuming that you can calculate such a bitboard quickly, how
do you use it to calculate the bishop's mobility?  A raw popcount is
obviously not enough, because all squares are not equally valuable.
And finally, you still have to look closely at all the blockers to
determine their importance.

I am not claiming that you are wrong, of course -- I am just curious
about how this is done with bitboards.

Tord



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