Author: Sune Fischer
Date: 07:46:17 02/06/04
Go up one level in this thread
On February 06, 2004 at 10:29:09, Tord Romstad wrote: >>You can mask out bad squares before you popcount, that's what I do currently. > >OK, but what I really want to know is how you find these bad squares >quickly. That depends on how you define the "bad" squares. It could be squares attacked by enemy pawns, it could be squares already defended by friendly pawns (we can assume that square is already under our control). Like wise you can define good squares for extra high mobility, e.g. squares near the enemy king, squares with enemy rooks and queens, advanced passed pawns, etc... I do something like that, still experimenting with the many posibilities :) >>>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. >> >>It's not so easy to figure out what the squares are worth. > >You're right. This is one of the reasons that good mobility is difficult >and (at least for non-bitboarders like me) expensive to do. Yeah sorry, I guess this point was already covered in another part of the thread, wrote before I had read everything :) >>Although an SME says you can't safely move there it might still be worth >>something to attack it. > >What's an SME? Static move evaluator, a generalization of SEE. > I agree that it's often worth something to attack a square >even if you cannot move there safely, but as I wrote elsewhere in the thread >this is reflected in other parts of the eval (space, mobility for the >opponent, pressure against opponent's king, etc.) > >>>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. >> >>You can easily mask out all the blocked pawns before you popcount, no problem. > >Yes, but not all blocked pawns are equal. Sometimes the pawn is easily >"unblocked", other times the blocker is almost impossible to remove. The question is if the search isn't better suited to handle some of these things. >Even though I have not yet given bitboards a try (I will some day), I >often try to think about how I would solve some specific evaluation >problem by using bitboards. Usually I find it tremendously difficult, >and this is quite often because bitboards do not distinguish between >different shades of gray. That's true, you need to build tables and find some way to index them if you want gray. The alternative is to loop through the bits you have found particularly interesting, e.g. pawns on 7th, and do a more careful analysis of those. At least you don't have to loop through all the pawns to find those on 7th :) > Each square has either a 1 or a 0, there >are no possible values in between. I don't want to know just whether >a pawn is blocked or not; I want a measure of how difficult it is to >remove the blocker. In an ideal world... :) Realisticly: * how much does it slow you down? * how accurate can you make it or is it at best still 30% noise? * are the scores big enough to really matter anyway? etc.. :) -S. >Tord
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