// 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
Score score = SCORE_ZERO;
// Undefended minors get penalized even if not under attack
- 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;
- }
+ 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);
++ score += single_bit(undefended) ? UndefendedMinorPenalty
++ : UndefendedMinorPenalty * 2;
// Enemy pieces not defended by a pawn and under our attack
- const Bitboard weakEnemies = pos.pieces(Them)
- & ~ei.attackedBy[Them][PAWN]
- & ei.attackedBy[Us][0];
+ Bitboard weakEnemies = pos.pieces(Them)
+ & ~ei.attackedBy[Them][PAWN]
+ & ei.attackedBy[Us][0];
if (!weakEnemies)
return score;