Introduce concept of double pawn protection.

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 38d5683493a5b14df76a7196a340b49a8b429ebd..e63d72e85e4d1e08602701e3c006ca17aae0718d 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -948,8 +948,8 @@ moves_loop: // When in check, search starts from here
                &&  pos.see_ge(move))
           extension = ONE_PLY;
 
-      else if (   pos.can_castle(us) // Extension for king moves that change castling rights
-               && type_of(movedPiece) == KING)
+      // Extension if castling
+      else if (type_of(move) == CASTLING)
           extension = ONE_PLY;
 
       // Calculate new depth for this move
@@ -1190,6 +1190,12 @@ moves_loop: // When in check, search starts from here
         // 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 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)