Author: JW de Kort
Date: 05:10:18 06/15/03
Go up one level in this thread
On June 14, 2003 at 19:34:12, Magoo wrote: >On June 14, 2003 at 17:11:11, JW de Kort wrote: > >>On June 14, 2003 at 10:30:58, Magoo wrote: >> >>>I did some tests last night, replacing my in_check() function with attack >>>tables, my thought was that it would be faster, but the result was not that >>>good, ok i did a fast hack, scanning the whole board because i dont have piece >>>lists, but my previous x-ray in_check function was huge. But now im wondering if >>>attack tables (implemented with piece lists) are that much better than x-ray. >>> >>>You have to check all pieces, = 8 pieces (king checks). >>>You have to check if pawns are promoted... = x pieces. >>>Check two squares in front of the king. >>> >>>And of course, sometimes you have to do some tracing.. (sliding pieces). >>>In the opening, middlegame there are usually pieces near the king, so the x-ray >>>based in_check only has to trace a few directions. >>>This got me thinking that the difference between the two isn't so big, am i >>>correct? maybe attacks are a few % faster? >> >>Hi, >> >>my in check is also a time consuming process. But is it absolutely necessery? >>Maybe it is possible not to check for check at all and just check if a capture >>removes the king one ply later. I have not tried this idea but maybe it is >>faster then using an in check. >> >>Also i'am thinking of implementing attack tables in my 0x88 program but i have >>not found a fast approach. Ant tips?> >> >>regards >> >>Jan Willem > >"Maybe it is possible not to check for check at all and just check if a capture >removes the king one ply later." > >Yes this is possible, but as i discoverd its really slow, in the early stages of >my program i did just what you say. The thing is if you are going to do a search >to depth D, you are really doing a search to depth D+1, which is much much >slower than doing a search to depth D and calling in_check() after each move. >If you don't have already implemented the "perft" command, i recommend you to do >it, it's a really good way to test the move generator. Depth 4 should only take >a second or two, Depth 5 i get 16 seconds (6 seconds are spent in in_check()). >Good programs do Depth 5 under 10 seconds. >About attack tables, if you already have piece lists, there is no harm trying it >(the code for creating the table is easy, and the modification to in_check is >also easy). > >But as I said in my first post i can't see how this would really improve the >time spent in in_check() in opening/middlegame positions. (the king has >pieces/pawns near => only a few directions have to be traced). Nice reply, thanks. In my program i use a piecelist. I used to do what you describe, checking for scheck starting at the position of the king. I found it more efficient to go through the piecelist of the opponent and only start 'sliding' if the piece of the opponent could move form to the square of teh king. This turned out to be faster than the methode you describe. As fot het attack table. I think that with an attack table only the attack status of the square of the king would have to be checked to see if there is a check. I think this would be faster than any routine. regards Jan Willem
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