Tweak CMH pruning

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 6a63fcaa338910a221d2770374faea8ead35f183..c589f2369c2cf72d256de89734cbae52d0d1c185 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -973,7 +973,7 @@ moves_loop: // When in check, search starts from here
               int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
 
               // Countermoves based pruning (~20 Elo)
-              if (   lmrDepth < 3 + ((ss-1)->statScore > 0)
+              if (   lmrDepth < 3 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
                   && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
                   && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
                   continue;
@@ -1185,15 +1185,12 @@ moves_loop: // When in check, search starts from here
 
         update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + ONE_PLY));
 
-        // Extra penalty for a quiet TT move in previous ply when it gets refuted
-        if ((ss-1)->moveCount == 1 && !pos.captured_piece())
-            update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+        // Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
+               if (   (ss-1)->moveCount == 1
+                   || ((ss-1)->currentMove == (ss-1)->killers[0] && (ss-1)->killers[0]))
+                   if (!pos.captured_piece())
+                update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
 
-        // Extra penalty for killer move in previous ply when it gets refuted
-        else if (  (ss-1)->killers[0]
-                && (ss-1)->currentMove == (ss-1)->killers[0]
-                && !pos.captured_piece())
-            update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth));
     }
     // Bonus for prior countermove that caused the fail low
     else if (   (depth >= 3 * ONE_PLY || PvNode)