On step 18 increase reduction by 2 if not ttmove and cutnode

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 55af6abab1c13bd4acba83b18d2744210cf967b8..f5eeb23b43f5c84cbfb81da457bc00726ac71027 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1215,6 +1215,10 @@ moves_loop: // When in check, search starts here
       // Step 18. Full depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1.
       else if (!PvNode || moveCount > 1)
       {
+               // Increase reduction for cut nodes and not ttMove (~1 Elo)
+               if (!ttMove && cutNode)
+                         r += 2;
+
                value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth - (r > 4), !cutNode);
       }