// 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
& (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
Bitboard weakEnemies = pos.pieces(Them)