Author: Peter Fendrich
Date: 04:22:47 01/02/03
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On January 02, 2003 at 06:12:24, Uri Blass wrote: >On January 02, 2003 at 05:27:32, Peter Fendrich wrote: > >>On January 02, 2003 at 05:00:06, Russell Reagan wrote: >> >>>I'm trying to nail down this bug in my move generator. I'm calculating perft for >>>positions and verifying them with other perft calculating engines. First I did >>>perft with only kings on the board, and things seemed fine. Then I added queens, >>>and things seemed fine. Then came the kings and rooks, and things seemed fine >>>when castling wasn't involved, but then I tried the following position: >>> >>>[D]r3k2r/8/8/8/8/8/8/R3K2R w KQkq - 0 1 >>> >>>Things stopped being fine. Other engines I tried got perft(4)=314346, but mine >>>gets perft(4)=314340, off by 6 nodes. Since there are *only* 26 legal moves in >>>the above position I set out to try each one, calculate perft, and find the >>>branch branch (or branches) containing the errors. >>> >>>The move Rb1 leads to a position that my engine incorrectly calculates perft 3. >>>So I had an incorrect perft 4, and I found one branch that has an incorrect >>>perft 3, so I'm on the right track (or so I thought). I tried each move from the >>>position after Rb1, and to my suprise not one move turned up an incorrect perft >>>1 or perft 2, which is what I was expecting. >>> >>>It seems like this shouldn't happen. Am I missing something? Or is this yet >>>another bug? >>> >>>Russell >> >>perft(4)=314340 is definitely a bug and you should also try perft 1 after Rb1. >>I would suspect problems with castling or king evasion if it was my program. >>Maybe you don't accept blacks o-o-o after Rb1? It is a legal move. >>Peter > >In that case perft 2 could be wrong from the initial position and it was not >wrong. That's true so it's probably not the problem. But with bugs you never know... weird side effects can happen and what's logical in normal situations are not logical when dealing with bugs. Peter
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