Adjust singular extension search depth

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index f9910fb72087dae7f4c2750fd748978d09c7f61d..abc6874e99583360a679ffe1cdad8806fee34861 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1024,10 +1024,9 @@ moves_loop: // When in check, search starts from here
               if (   lmrDepth < 6
                   && !inCheck
                   && ss->staticEval + 235 + 172 * lmrDepth <= alpha
-                  &&  thisThread->mainHistory[us][from_to(move)]
-                    + (*contHist[0])[movedPiece][to_sq(move)]
+                  &&  (*contHist[0])[movedPiece][to_sq(move)]
                     + (*contHist[1])[movedPiece][to_sq(move)]
-                    + (*contHist[3])[movedPiece][to_sq(move)] < 25000)
+                    + (*contHist[3])[movedPiece][to_sq(move)] < 27400)
                   continue;
 
               // Prune moves with negative SEE (~20 Elo)
@@ -1056,9 +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)
@@ -1150,7 +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)
           {
@@ -1194,10 +1193,16 @@ moves_loop: // When in check, search starts from here
 
           value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
 
-          doFullDepthSearch = (value > alpha && d != newDepth), didLMR = true;
+          doFullDepthSearch = value > alpha && d != newDepth;
+
+          didLMR = true;
       }
       else
-          doFullDepthSearch = !PvNode || moveCount > 1, didLMR = false;
+      {
+          doFullDepthSearch = !PvNode || moveCount > 1;
+
+          didLMR = false;
+      }
 
       // Step 17. Full depth search when LMR is skipped or fails high
       if (doFullDepthSearch)