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Subject: Re: Question for Hyatt about Alpha/Beta

Author: Anthony Cozzie

Date: 06:08:28 02/06/04

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On February 06, 2004 at 07:22:19, Tord Romstad wrote:

>On February 06, 2004 at 06:06:07, Vasik Rajlich wrote:
>
>>Interesting discussion. One other thing to throw in: it seems to me that a
>>rook's mobility being hindered by a pawn is more serious than a bishop's
>>mobility being hindered by a pawn, because it's easier to move a pawn off of a
>>diagonal (ie just push the pawn) than to move it away from a file. So, it makes
>>some sense to emphasize rooks on open files (rather than rook mobility), and to
>>give this a higher value than a bishop on an open diagonal. Ideally, a bishop's
>>diagonal would be evaluated to see how easy it is for any blocking pawns to
>>move, because sometimes a bishop can be totally without prospects because of one
>>pawn.
>
>Yes, it is essential to consider which pawns are blocked and unblocked when
>doing mobility evaluation, especially for bishops.
>
>>Also, it doesn't seem super-cheap cheap to get bishop mobility, you need to do a
>>CountBitboardBits (), while open file is just an "&" operation and a boolean
>>test.
>
>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.
>
>Tord


With rotated bitboards it is practically free; it is just a popcount8.

Basically just popcount your index.

anthony



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