X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=d04898e8570a13486f0b11088760138d4d5c768a;hb=559942d64de9497c9d6d13b22307b4b9e1ce8ecf;hp=f634b2d2d67b97beaf9a67d97f50b709f509cb86;hpb=0b7cc8bd2f5a51de9f911fcdfb253b1c9f513897;p=stockfish

diff --git a/src/search.cpp b/src/search.cpp
index f634b2d2..d04898e8 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -610,10 +610,11 @@ namespace {
 
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
 
-    (ss+1)->ttPv = false;
+    (ss+1)->ttPv         = false;
     (ss+1)->excludedMove = bestMove = MOVE_NONE;
-    (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
-    Square prevSq = to_sq((ss-1)->currentMove);
+    (ss+2)->killers[0]   = (ss+2)->killers[1] = MOVE_NONE;
+    ss->doubleExtensions = (ss-1)->doubleExtensions;
+    Square prevSq        = to_sq((ss-1)->currentMove);
 
     // Initialize statScore to zero for the grandchildren of the current position.
     // So statScore is shared between all grandchildren and only the first grandchild
@@ -1074,7 +1075,11 @@ moves_loop: // When in check, search starts from here
           {
               extension = 1;
               singularQuietLMR = !ttCapture;
-              if (!PvNode && value < singularBeta - 93)
+
+              // Avoid search explosion by limiting the number of double extensions to at most 3
+              if (   !PvNode
+                  && value < singularBeta - 93
+                  && ss->doubleExtensions < 3)
                   extension = 2;
           }
 
@@ -1105,6 +1110,7 @@ moves_loop: // When in check, search starts from here
 
       // Add extension to new depth
       newDepth += extension;
+      ss->doubleExtensions = (ss-1)->doubleExtensions + (extension == 2);
 
       // Speculative prefetch as early as possible
       prefetch(TT.first_entry(pos.key_after(move)));
@@ -1132,6 +1138,9 @@ moves_loop: // When in check, search starts from here
       {
           Depth r = reduction(improving, depth, moveCount);
 
+          if (PvNode)
+              r--;
+
           // Decrease reduction if the ttHit running average is large (~0 Elo)
           if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024)
               r--;
@@ -1461,7 +1470,7 @@ moves_loop: // When in check, search starts from here
 
     // Initialize a MovePicker object for the current position, and prepare
     // to search the moves. Because the depth is <= 0 here, only captures,
-    // queen and checking knight promotions, and other checks(only if depth >= DEPTH_QS_CHECKS)
+    // queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS)
     // will be generated.
     MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
                                       &thisThread->captureHistory,