Verified SEE pruning for capturing and checking moves.

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 17c1c28b2646eadd6ec565892f7f0a39620a92a4..7564c10983e32e6aa4ab80d88d4b5af9bb496c97 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1019,9 +1019,27 @@ moves_loop: // When in check, search starts here
                    + captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 7 < alpha)
                   continue;
 
+              Bitboard occupied;
               // SEE based pruning (~11 Elo)
-              if (!pos.see_ge(move, Value(-206) * depth))
-                  continue;
+              if (!pos.see_ge(move, occupied, Value(-206) * depth))
+              {
+                  if (depth < 2 - capture)
+                      continue;
+                  // don't prune move if a heavy enemy piece (KQR) is under attack after the exchanges
+                  Bitboard leftEnemies = (pos.pieces(~us, QUEEN, ROOK) | pos.pieces(~us, KING)) & occupied;
+                  Bitboard attacks = 0;
+                  occupied |= to_sq(move);
+                  while (leftEnemies && !attacks)
+                  {
+                      Square sq = pop_lsb(leftEnemies);
+                      attacks |= pos.attackers_to(sq, occupied) & pos.pieces(us) & occupied;
+                      // exclude Queen/Rook(s) which were already threatened before SEE
+                      if (attacks && (sq != pos.square<KING>(~us) && (pos.attackers_to(sq, pos.pieces()) & pos.pieces(us))))
+                          attacks = 0;
+                  }
+                  if (!attacks)
+                      continue;
+              }
           }
           else
           {
@@ -1047,8 +1065,9 @@ moves_loop: // When in check, search starts here
 
               lmrDepth = std::max(lmrDepth, 0);
 
+              Bitboard occupied;
               // Prune moves with negative SEE (~4 Elo)
-              if (!pos.see_ge(move, Value(-24 * lmrDepth * lmrDepth - 15 * lmrDepth)))
+              if (!pos.see_ge(move, occupied, Value(-24 * lmrDepth * lmrDepth - 15 * lmrDepth)))
                   continue;
           }
       }
@@ -1533,6 +1552,7 @@ moves_loop: // When in check, search starts here
                                       prevSq);
 
     int quietCheckEvasions = 0;
+    Bitboard occupied;
 
     // Step 5. Loop through all pseudo-legal moves until no moves remain
     // or a beta cutoff occurs.
@@ -1569,7 +1589,7 @@ moves_loop: // When in check, search starts here
               continue;
           }
 
-          if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
+          if (futilityBase <= alpha && !pos.see_ge(move, occupied, VALUE_ZERO + 1))
           {
               bestValue = std::max(bestValue, futilityBase);
               continue;
@@ -1588,7 +1608,7 @@ moves_loop: // When in check, search starts here
           continue;
 
       // Do not search moves with bad enough SEE values (~5 Elo)
-      if (!pos.see_ge(move, Value(-110)))
+      if (!pos.see_ge(move, occupied, Value(-110)))
           continue;
     }