Introduce capture history pruning

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index cfda94b8080110112b1bac35b20472fd09719e22..dba8857efdacee98ab84a2e075b9af0e97593e2e 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -789,6 +789,8 @@ namespace {
         }
     }
 
+    CapturePieceToHistory& captureHistory = thisThread->captureHistory;
+
     // Step 6. Static evaluation of the position
     if (inCheck)
     {
@@ -899,7 +901,7 @@ namespace {
         &&  abs(beta) < VALUE_TB_WIN_IN_MAX_PLY)
     {
         Value raisedBeta = std::min(beta + 189 - 45 * improving, VALUE_INFINITE);
-        MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &thisThread->captureHistory);
+        MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &captureHistory);
         int probCutCount = 0;
 
         while (  (move = mp.next_move()) != MOVE_NONE
@@ -954,7 +956,7 @@ moves_loop: // When in check, search starts from here
 
     MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
                                       &thisThread->lowPlyHistory,
-                                      &thisThread->captureHistory,
+                                      &captureHistory,
                                       contHist,
                                       countermove,
                                       ss->killers,
@@ -1010,12 +1012,12 @@ moves_loop: // When in check, search starts from here
           // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
           moveCountPruning = moveCount >= futility_move_count(improving, depth);
 
+          // Reduced depth of the next LMR search
+          int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
+
           if (   !captureOrPromotion
               && !givesCheck)
           {
-              // Reduced depth of the next LMR search
-              int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
-
               // Countermoves based pruning (~20 Elo)
               if (   lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
                   && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
@@ -1035,8 +1037,16 @@ moves_loop: // When in check, search starts from here
               if (!pos.see_ge(move, Value(-(32 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
                   continue;
           }
-          else if (!pos.see_ge(move, Value(-194) * depth)) // (~25 Elo)
-              continue;
+          else
+          {
+              if (   !givesCheck
+                  && lmrDepth < 1
+                  && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
+                  continue;
+
+              if (!pos.see_ge(move, Value(-194) * depth)) // (~25 Elo)
+                  continue;
+          }
       }
 
       // Step 14. Extensions (~75 Elo)