Introduce countermove based pruning for qsearch

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 266e2db30d0f2516abeb078a894cce3e16136d39..2ca64a0167ebf93e99ab83991c2608b217d3f451 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1570,6 +1570,12 @@ moves_loop: // When in check, search starts from here
                                                                 [pos.moved_piece(move)]
                                                                 [to_sq(move)];
 
+      if (  !captureOrPromotion
+          && moveCount >= abs(depth) + 1
+          && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold
+          && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold)
+          continue;
+
       // Make and search the move
       pos.do_move(move, st, givesCheck);
       value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - 1);