MadChess 3.1 Beta 0c601ea (Singular Move)

I strengthened MadChess by extending the search horizon of singular moves. I gleaned the idea from the Stockfish chess engine.

Quoting from my Pull Request #17:

• In the GetSearchHorizon method, added call to a new method, IsBestMoveSingular, that determines if best move that had failed high in recent searches is best by a significant margin.
• If so, extend the search by one ply. A code comment explains why:
• The best move (from the cache) is singular. That is, it’s the only good move in the position.
• Evaluation of the current position relies on the accuracy of the singular move’s score.
• If the engine misjudges the singular move, the position could deteriorate because no alternative strong moves exist.
• To increase confidence in the singular move’s score, search it one ply deeper.

In addition, in Pull Request #16 I implemented asymptotic history scores. This simplifies keeping history scores within defined bounds. Also I fixed a bug in the Standard Algebraic Notation (SAN) parser for positions where the moving piece is disambiguated by square (not merely by rank or file). These changes improved code quality but did not increase playing strength.

Singular move increased the playing strength of MadChess 3.1 Beta by 13 Elo.

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