Penalty for undefended rook as well

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index ef52f7479d678b2c95ce4249fdd394a27f3f0971..c03aa99f51940f0f0ec96fcbc7dce8b5ec9b4e69 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -167,6 +167,9 @@ namespace {
   // happen in Chess960 games.
   const Score TrappedBishopA1H1Penalty = make_score(100, 100);
 
+  // Penalty for BNR that is not defended by anything
+  const Score UndefendedPiecePenalty = make_score(25, 10);
+
   // The SpaceMask[Color] contains the area of the board which is considered
   // by the space evaluation. In the middle game, each side is given a bonus
   // based on how many squares inside this area are safe and available for
@@ -679,12 +682,22 @@ Value do_evaluate(const Position& pos, Value& margin) {
     Bitboard b;
     Score score = SCORE_ZERO;
 
+    // Undefended pieces get penalized even if not under attack
+    Bitboard undefended = pos.pieces(Them) & ~ei.attackedBy[Them][0];
+    const Bitboard undefendedMinors = undefended & (pos.pieces(BISHOP) | pos.pieces(KNIGHT));
+    
+    if (undefendedMinors)
+        score += single_bit(undefendedMinors) ? UndefendedPiecePenalty
+                                              : UndefendedPiecePenalty * 2;
+    if (undefended & pos.pieces(ROOK))
+        score += UndefendedPiecePenalty;
+
     // Enemy pieces not defended by a pawn and under our attack
     Bitboard weakEnemies =  pos.pieces(Them)
                           & ~ei.attackedBy[Them][PAWN]
                           & ei.attackedBy[Us][0];
     if (!weakEnemies)
-        return SCORE_ZERO;
+        return score;
 
     // Add bonus according to type of attacked enemy piece and to the
     // type of attacking piece, from knights to queens. Kings are not