// 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);
+ // 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
Bitboard b;
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 += single_bit(undefended) ? UndefendedMinorPenalty
- : UndefendedMinorPenalty * 2;
+ // 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)