MadChess 3.0 Beta 2d855ec (Crash Bug)

I found and exterminated a bug that caused MadChess to crash in about one quarter of one percent of games. I noticed the engine crashes on line 6 of this code in the Board.IsMoveLegal(ref ulong Move) method. First Hypothesis : Illegal Move Causing King Capture? I suspected the crash was caused by kingSquare == Square.Illegal (meaning king not on any square) due to a missing king. Perhaps a move two ply earlier exposed its own king to check, MadChess erroneously considered the move legal, then captured the king the previous ply? If that were true, in the current ply, when… Continue Reading

MadChess 3.0 Beta 6794c89 (King Safety)

I added evaluation of king safety to MadChess 3.0 Beta. Because determining the safety of a king’s position involves examining moves that attack squares near the king, I combined it with piece mobility evaluation, which also examines moves. When examining piece mobility, keep a weighted count of attacks on squares ringing the king (16 squares in outer ring and 8 squares in inner ring) with separate weights for attacks by minor pieces, rooks, and queens. In the following code, white moves to squares ringing the black king contribute negatively to black’s king safety. Black moves to squares ringing the white… Continue Reading

MadChess 3.0 Beta bef88d5 (Tweak Search, Tune Eval)

I’ll let my Pull Request notes (PR 3) explain where I began and where I finished (hint: not where I expected) with my latest code improvements to MadChess 3.0 Beta: Originally, I intended this PR to add Static Exchange Evaluation (SEE) to MadChess’ search method to reorder or skip evaluation of captures and / or quiet moves that enable the opponent to profitably capture the most recently moved piece. After numerous attempts to write a method that evaluates piece exchanges- either statically (without actually moving pieces) or dynamically (move pieces and search), and integrate it into the search, I could… Continue Reading

MadChess 3.0 Beta 6f3d17a (Late Move Pruning)

I added late move pruning to MadChess 3.0 Beta. Quiet moves (not captures, pawn promotions, castling, or check) near the search horizon that are sorted near the bottom of the move list- in order words, “late” moves- are skipped. These moves are “late” because history heuristics have recorded few instances of them causing a beta cutoff. Most likely they are futile (they will not raise the score to alpha), so the engine doesn’t waste time searching them. The search only examines two quiet moves immediately next to the search horizon, five quiet moves two ply from the horizon, up to… Continue Reading

MadChess 3.0 Beta 5c5d4fc (Piece Mobility)

I have not worked on my chess engine in over a year. I had other, more important, priorities. In the last year, my wife and I bought a new home closer to the city, sold our old home, moved (*), started new jobs in the summer, and ran the Chicago Marathon in the autumn. The little free time I had for hobby programming I spent on general interest projects, not on MadChess. I’m especially proud of Leaderless Replication, an essay I published on my general programming blog, ErikTheCoder. Lately I’ve had time to do some chess programming. I added piece… Continue Reading