Author: Erik Madsen

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MadChess 3.0 Beta 42d7702 (Position Cache Optimization)

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Quoting from my Pull Request #12: Converted Cache class’ _positions field from a jagged array to a flat array. The flat array is more memory efficient than a jagged array. Jagged arrays have a .NET object header for each sub-array (for garbage collection tracking of reachable-from-root). This enables more positions to be stored per megabyte of memory. The code in this PR stores 65,536 positions per MB = 8,388,608 positions for a typically sized 128 MB cache. Added stats to track cache hit %, best move found in cached position %, and count of invalid best moves. Stats are displayed… Continue Reading

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MadChess 3.0 Beta 22002dc (Move Generation Optimization)

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Rather than repeat myself, I’ll explain my recent code update by copying the text of my Pull Request #10 here: Improved detection of pieces pinned to own king by sliding attackers. Previous implementation only found potentially pinned pieces (because the pieces were on the same file, rank, or diagonal as the sliding attacker). The new implementation finds all actually pinned pieces. This speeds up resolution of pseudo-legal moves to legal moves by eliminating unnecessary calls to Board.IsSquareAttacked(kingSquare) in Board.IsMoveLegal method. Its benefit is limited though because many pseudo-legal moves never are examined for legality because a beta cutoff occurs before… Continue Reading

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MadChess 3.0 Beta f231dac (PVS and Null Move Improvements)

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I improved MadChess 3.0 Beta’s Principal Variation Search (PVS) by consolidating two separate re-searches into one. In addition, I changed the null move implementation so it reduces the search horizon more aggressively if the current position’s static score far exceeds beta. Previously, if a PVS search failed high, the engine would confirm the fail high first by restoring beta from bestScore + 1 to its original value and re-searching. If that also failed high, it restored the search horizon from a reduced value to its original value and re-searched. If that failed high the engine took a beta cutoff. I… Continue Reading

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Play Rather Than Code

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Watching The Queen’s Gambit on Netflix nudged me to play chess online. I’ve spent time on chess over the last few years… programming an engine, not actually playing. I’m very rusty. Though my puzzle rating is decent. It’s much higher than my game rating, suggesting I need to work on time management. Thinking fast is not my strength, but everyone online plays blitz or bullet so here goes nothing… Last night I joined a bullet tournament with a 2+1 clock. Each player has 2 minutes to make all their moves in the game, plus 1 second added to their clock… Continue Reading

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Knight Outpost

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A knight positioned on an outpost controls opponent territory, restricting movement of the opponent’s pieces on the opponent’s side of the board. An outpost is defined as a square on the fifth or sixth rank, occupied by a minor piece (usually a knight), supported by its own pawn, and positioned such that it cannot ever be attacked by an opposing pawn. In other words, the opponent has no pawns on the neighboring files, or if the opponent has pawns on the neighboring files, they’ve advanced even with or beyond the outpost square. Red highlights in the above position indicate squares… Continue Reading