Bonus for loose enemies

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index d8017065f0941b009e5d917da2f07d25a3a79ede..a63b40ae98403a69153a2782c1bd066c75f2d153 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -185,6 +185,7 @@ namespace {
   const Score TrappedRook         = S(92,  0);
   const Score Checked             = S(20, 20);
   const Score ThreatByHangingPawn = S(70, 63);
+  const Score LooseEnemies        = S( 0, 25);
   const Score Hanging             = S(48, 28);
   const Score ThreatByPawnPush    = S(31, 19);
   const Score Unstoppable         = S( 0, 20);
@@ -469,6 +470,11 @@ namespace {
     Bitboard b, weak, defended, safeThreats;
     Score score = SCORE_ZERO;
 
+    // Small bonus if the opponent has loose pawns or pieces
+    if (   (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
+        & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
+        score += LooseEnemies;
+
     // Non-pawn enemies attacked by a pawn
     weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];