Decrease reduction in case we had singular extension. #2146

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 5d6babb45f716200c82dd30b2265d9857a0e81b3..f021f8ff5eb183517a9391bd6cff6faee74d571c 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -855,6 +855,7 @@ moves_loop: // When in check, search starts from here
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
     moveCountPruning = false;
     ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+    int singularExtensionLMRmultiplier = 0;
 
     // Step 12. Loop through all pseudo-legal moves until no moves remain
     // or a beta cutoff occurs.
@@ -911,7 +912,12 @@ moves_loop: // When in check, search starts from here
           ss->excludedMove = MOVE_NONE;
 
           if (value < singularBeta)
+              {
               extension = ONE_PLY;
+              singularExtensionLMRmultiplier++;
+              if (value < singularBeta - std::min(3 * depth / ONE_PLY, 39))
+                 singularExtensionLMRmultiplier++;
+              }
 
           // Multi-cut pruning
           // Our ttMove is assumed to fail high, and now we failed high also on a reduced
@@ -1021,6 +1027,8 @@ moves_loop: // When in check, search starts from here
           // Decrease reduction if opponent's move count is high (~10 Elo)
           if ((ss-1)->moveCount > 15)
               r -= ONE_PLY;
+          // Decrease reduction if move has been singularly extended
+          r -= singularExtensionLMRmultiplier * ONE_PLY;
 
           if (!captureOrPromotion)
           {