MadChess 3.1 Beta 533e382 (Move Legality Performance Improvement)

I improved the performance of code that determines the legality of pseudo-legal moves. Previously, move legality was tested prior to playing a move. This consisted of playing a move (to test whether it exposed its own king to check and whether it delivered check on the enemy king), undoing the move, updating the “check” move property, then re-playing the move. Now a move is played, move legality and check is tested, and the Board.PlayMove method returns a (bool isLegal, bool deliversCheck) tuple.

The calling method (such as Search.GetDynamicScore or Search.GetQuietScore) then either 1) undoes the move (if illegal or futile) and continues to the next pseudo-legal move or 2) searches the resulting position.

In addition to move legality, I experimented with other performance improvements. None of these experiments succeeded except PR 33: Trust Move Capture Victim, which eliminated redundant calls to Position.GetPiece(Square square) in move generation and when playing moves.

Eliminating redundant double-playing of a move (to test move legality) during search increased the search speed of MadChess 3.1 Beta and produced a 36 Elo gain in playing strength.

1. GitHub commit (hash) or Subversion source code revision (integer)
2. Win At Chess position test, 3 seconds per position
3. Bullet chess, 2 min / game + 1 sec / move