Anchored bishops

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 40630d22e314ab0c691fe2fe5f475195816a8b21..fad2a785acccfb26be33b7c138862f0304fde91d 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -308,11 +308,12 @@ namespace {
             if (Pt == BISHOP)
             {
                 // Penalty according to number of pawns on the same color square as the
-                // bishop, bigger when the center files are blocked with pawns.
+                // bishop, bigger when the center files are blocked with pawns and smaller
+                // when the bishop is outside the pawn chain.
                 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
 
                 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
-                                     * (1 + popcount(blocked & CenterFiles));
+                                     * (!bool(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
 
                 // Bonus for bishop on a long diagonal which can "see" both center squares
                 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))