Author: Robert Hyatt
Date: 12:47:05 03/02/03
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On March 02, 2003 at 12:15:19, Tom Likens wrote: > >I ran across an interesting bug the other day that I thought I'd share >and also get some advice on. I hash the scores and moves that I get >from the tablebases during a search. For a normal draw (i.e. a non- >stalemate draw) I simply store any move that maintains the draw in both >the hash table and the principal variation. > >The problem I ran into is that when a stalemate is encountered, there is >no move to store. This has the potential to corrupt the hash table. >Unfortunately, since the tablebase only returns a 0 for a draw, there is >no easy way to differentiate between the two types of draws. I'm curious >how other people handle this problem. I can think of a couple of >solutions, but none that are completely satisfactory. > >1. Whenever a draw is returned from the tablebase verify that it is > or is not a stalemate. If it is a stalemate, skip the storage step. > This is accurate and works, but it's slow. I don't understand the problem. You advance to ply N+1 after making a move at ply N. You do a repetition check. If it returns "true" you have no move to store, just a score although I don't store at this position since the rep test is done first and there's no point. But, then you probe the egtb tables, and if you get a hit, there is no best move either at this ply. You just store the score, a best=0, and back up to the previous ply where there _is_ a best move... Maybe you are doing something different??? > >2. If a draw score is returned, check if the side with the right to move > has only a lone king. If yes, then also skip the storage of the move. > This is faster, but it is not completely accurate since it could miss > a variety of stalemate positions. > >I'm probably missing something trivial so any thoughts and/or comments >would be welcome. > >regards, >--tom
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