Dev Builds » 20181224-0944

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Commit ID 96ac85b3196ed7369a91a0852da0adcaf05a04b3
Author protonspring
Date 2018-12-24 09:44:38 UTC
Improve endgame KBN vs K (#1877) Even when playing without endgame table bases, this particular endgame should be a win 100% of the time when Stockfish is given a KRBK position, assuming there are enough moves remaining in the FEN to finish the game without hitting the 50 move rule. PROBLEM: The issue with master here is that the PushClose difference per square is 20, however, the difference in squares for the PushToCorners array is usually less. Thus, the engine prefers to move the kings closer together rather than pushing the weak king to the correct corner. What happens is if the weak king is in a safe corner, SF still prefers pushing the kings together. Occasionally, the strong king traps the weak king in the safe corner. It takes a while for SF to figure it out, but often draws the game by the 50 move rule (on shorter time controls). This patch increases the PushToCorners values to correct this problem. We also added an assert to catch any overflow problem if anybody would want to increase the array values again in the future. It was tested in a couple of matches starting with random KRBK positions and showed increased winning rates, see No functional change
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