Adjust singular extension search depth

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index a54e181a2a906e1033848d9983655a7805eb24cf..abc6874e99583360a679ffe1cdad8806fee34861 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1055,9 +1055,9 @@ moves_loop: // When in check, search starts from here
           &&  pos.legal(move))
       {
           Value singularBeta = ttValue - (((ttPv && !PvNode) + 4) * depth) / 2;
-          Depth halfDepth = depth / 2;
+          Depth singularDepth = (depth - 1 + 3 * (ttPv && !PvNode)) / 2;
           ss->excludedMove = move;
-          value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, halfDepth, cutNode);
+          value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
           ss->excludedMove = MOVE_NONE;
 
           if (value < singularBeta)
@@ -1149,7 +1149,7 @@ moves_loop: // When in check, search starts from here
 
           // Decrease reduction if ttMove has been singularly extended (~3 Elo)
           if (singularLMR)
-              r -= 2;
+              r -= 1 + (ttPv && !PvNode);
 
           if (!captureOrPromotion)
           {