Author: Bas Hamstra
Date: 06:31:56 10/18/00
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On October 17, 2000 at 10:02:54, Robert Hyatt wrote: >On October 17, 2000 at 05:14:14, Bas Hamstra wrote: > >>On October 16, 2000 at 10:18:31, Robert Hyatt wrote: >> >>>On October 16, 2000 at 06:32:53, Pham Minh Tri wrote: >>> >>>>I know that Bitboard makes move generation the fastest, but this structure is >>>>also one of the most complicated. However, an old post said that the generation >>>>function is not the key of success to chess program and the author illustrated >>>>that after his optimality (which made that function work much faster), the speed >>>>of system increased only 1 percent. >>>> >>>>As a result, my question is: is bitboard really worthy for implementation when >>>>it takes a long time to program and more time to fix all bugs (maybe several >>>>times bigger than the rest of program)? Or is it better if we use this time to >>>>concentrate on hash table, null move threshold and so on? I plan that I will >>>>forget the bitboard (at least in the first period) if it help me only few >>>>percent. >>>> >>>>Pham >>> >>> >>>I see nothing that makes them harder to use than an array. Nor nothing that >>>makes them particularly easier to use either. >>> >>>They have certain advantages on new architectures that move 64 bits of data >>>around in one cycle, and they have some advantages in evaluation where you can >>>answer lots of questions in one AND or OR operation. On current machines, I >>>would say they are no faster nor slower than any other approach. On 64 bit >>>architectures, they begin to look better. >> >>Well if you wanted to build attacked-from tables I would not be so sure. Some >>programs use that kind of info extensively. If you wanted to make such a >>program, BB certainly wouldn't be the first option. >> >>However I know at least 1 program that builds attacks-to tables with BB and that >>seems to work fine. >> >> >>Bas Hamstra. > > >Attacks_from works fine in bitboards. Just read the chess 4.x article in >"Chess Skill in Man and Machine". I did them until I decided I didn't really >need that often enough to tolerate the overhead. I _still_ get that information >very quickly if I want it... but I could get it even quicker. Early versions >of crafty had attacks_from and attacks_to that were incrementally updated as the >board was modified. I changed to rotated bitmaps to eliminate the overhead of >the incremental update and turn attacks into a simple table lookup. And I got >rid of attacks_from almost everywhere except for a couple of places where I > compute "in check". I know you don't use them. So it is logical you leave them out. But not all program's work like Crafty. There are a couple of programs that use attacked-from info heavily. They want to know not only that a square is attacked, but exactly by what. For many squares. Now I personally think that if you wanted to do this, you better not use the rotated BB approach. Regards, Bas.
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