Do more futility pruning in qsearch

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index a745d3bfdd0ed16933a9d53dcd8f7ab830637940..beb1cb54822856df2c7522a0a3f0f0f07e0d88b2 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1549,17 +1549,29 @@ moves_loop: // When in check, search starts here
 
                 futilityValue = futilityBase + PieceValue[pos.piece_on(to_sq(move))];
 
+                // If static eval + value of piece we are going to capture is much lower
+                // than alpha we can prune this move
                 if (futilityValue <= alpha)
                 {
                     bestValue = std::max(bestValue, futilityValue);
                     continue;
                 }
 
+                // If static eval is much lower than alpha and move is not winning material
+                // we can prune this move
                 if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
                 {
                     bestValue = std::max(bestValue, futilityBase);
                     continue;
                 }
+
+                // If static exchange evaluation is much worse than what is needed to not
+                // fall below alpha we can prune this move
+                if (futilityBase > alpha && !pos.see_ge(move, (alpha - futilityBase) * 4))
+                {
+                    bestValue = alpha;
+                    continue;
+                }
             }
 
             // We prune after the second quiet check evasion move, where being 'in check' is