Optimize undefended minor check.

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 2193eb6be797805b6aa46a4f510bbc9c14c4a38c..9bd403e1bf8ab1100284eec6d27f791f5b3b6bcc 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 a minor piece that is not defended by anything
+  const Score UndefendedMinorPenalty = 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
@@ -680,16 +683,19 @@ Value do_evaluate(const Position& pos, Value& margin) {
     Score score = SCORE_ZERO;
 
     // Undefended minors get penalized even if not under attack
-    Bitboard undefended =  pos.pieces(Them)
-                         & (pos.pieces(BISHOP) | pos.pieces(KNIGHT))
-                         & ~ei.attackedBy[Them][0];
-    if (undefended)
-        score += make_score(25, 10) * popcount<Max15>(undefended);
+    const Bitboard undefended =  pos.pieces(Them)
+                              & (pos.pieces(BISHOP) | pos.pieces(KNIGHT))
+                              & ~ei.attackedBy[Them][0];
+    if (undefended) {
+        score += UndefendedMinorPenalty;
+        if (!single_bit(undefended))
+            score += UndefendedMinorPenalty;
+    }
 
     // Enemy pieces not defended by a pawn and under our attack
-    Bitboard weakEnemies =  pos.pieces(Them)
-                          & ~ei.attackedBy[Them][PAWN]
-                          & ei.attackedBy[Us][0];
+    const Bitboard weakEnemies =  pos.pieces(Them)
+                               & ~ei.attackedBy[Them][PAWN]
+                               & ei.attackedBy[Us][0];
     if (!weakEnemies)
         return score;