Author: Uri Blass
Date: 03:12:24 01/02/03
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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. Uri
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