New default net nn-3b20abec10c1.nnue

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 5306bb9a0084b2ee50ae7b4fc83cbd7324ba2bd0..9bba563a7796ba7ac0f5191e1c804a9f8998bbf9 100644 (file)
--- 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
@@ -953,6 +954,7 @@ moves_loop: // When in check, search starts from here
 
     value = bestValue;
     singularQuietLMR = moveCountPruning = false;
+    bool doubleExtension = false;
 
     // Indicate PvNodes that will probably fail low if the node was searched
     // at a depth equal or greater than the current depth, and the result of this search was a fail low.
@@ -1074,8 +1076,15 @@ 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;
+                  doubleExtension = true;
+              }
           }
 
           // Multi-cut pruning
@@ -1105,6 +1114,7 @@ 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)));
@@ -1147,7 +1157,6 @@ moves_loop: // When in check, search starts from here
 
           // Increase reduction at root and non-PV nodes when the best move does not change frequently
           if (   (rootNode || !PvNode)
-              && thisThread->rootDepth > 10
               && thisThread->bestMoveChanges <= 2)
               r++;
 
@@ -1182,8 +1191,8 @@ moves_loop: // When in check, search starts from here
 
           // In general we want to cap the LMR depth search at newDepth. But if
           // reductions are really negative and movecount is low, we allow this move
-          // to be searched deeper than the first move.
-          Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && moveCount <= 5));
+          // to be searched deeper than the first move, unless ttMove was extended by 2.
+          Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && moveCount <= 5 && !doubleExtension));
 
           value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);