Perfect Perft!

Over the weekend I got the last couple of bugs out of Maverick perft routine.  It now has a perfect node match for all the positions I’ve tried – Yippee!! 

In my opinion getting to this stage is a major milestone in the development of a chess engine.  If you can get this far you’re almost certainly capable of writing a fully functional chess engine.

It may be interesting to some to share my approach to perft.  When finding positions to use in a perft test you need to come up with “odd” position – ones which don’t occur too often and ones which are special cases.  Normally this means positions which contain the special chess moves i.e. castling, en-passant, promotions and capture promotions.  In particular I’ve found the best positions for perft are those which involve getting into, or out of, check using these special moves.  Also position with lots of revealed checks, pinned pieces are good.

Here’s the list of positions I used.  They are gleaned from Chess Programming on Wikispaces and this post on CCC:

http://chessprogramming.wikispaces.com/Perft+Results

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1; perft 6 = 119060324

r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq -; perft 5 = 193690690


8/2p5/3p4/KP5r/1R3p1k/8/4P1P1/8 w - -; perft 7 = 178633661


r3k2r/Pppp1ppp/1b3nbN/nP6/BBP1P3/q4N2/Pp1P2PP/R2Q1RK1 w kq - 0 1; perft 6 = 706045033


1k6/1b6/8/8/7R/8/8/4K2R b K - 0 1; perft 5 = 1063513

TalkChess PERFT Tests (by Martin Sedlak)

//--Illegal ep move #1


3k4/3p4/8/K1P4r/8/8/8/8 b - - 0 1; perft 6 = 1134888


//--Illegal ep move #2


8/8/4k3/8/2p5/8/B2P2K1/8 w - - 0 1; perft 6 = 1015133


//--EP Capture Checks Opponent


8/8/1k6/2b5/2pP4/8/5K2/8 b - d3 0 1; perft 6 = 1440467


//--Short Castling Gives Check


5k2/8/8/8/8/8/8/4K2R w K - 0 1; perft 6 = 661072


//--Long Castling Gives Check


3k4/8/8/8/8/8/8/R3K3 w Q - 0 1; perft 6 = 803711


//--Castle Rights


r3k2r/1b4bq/8/8/8/8/7B/R3K2R w KQkq - 0 1; perft 4 = 1274206


//--Castling Prevented


r3k2r/8/3Q4/8/8/5q2/8/R3K2R b KQkq - 0 1; perft 4 = 1720476


//--Promote out of Check


2K2r2/4P3/8/8/8/8/8/3k4 w - - 0 1; perft 6 = 3821001


//--Discovered Check


8/8/1P2K3/8/2n5/1q6/8/5k2 b - - 0 1; perft 5 = 1004658


//--Promote to give check


4k3/1P6/8/8/8/8/K7/8 w - - 0 1; perft 6 = 217342


//--Under Promote to give check


8/P1k5/K7/8/8/8/8/8 w - - 0 1; perft 6 = 92683


//--Self Stalemate


K1k5/8/P7/8/8/8/8/8 w - - 0 1; perft 6 = 2217


//--Stalemate & Checkmate


8/k1P5/8/1K6/8/8/8/8 w - - 0 1; perft 7 = 567584    


//--Stalemate & Checkmate


8/8/2k5/5q2/5n2/8/5K2/8 b - - 0 1; perft 4 = 23527

Tomorrow I’ll talk about the perft debugging process – it’s quite simple once you put a couple of things in place!