// 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
if (Piece == KNIGHT || Piece == QUEEN)
b = pos.attacks_from<Piece>(s);
else if (Piece == BISHOP)
- b = attacks_bb<BISHOP>(s, pos.occupied_squares() & ~pos.pieces(QUEEN, Us));
+ b = attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN, Us));
else if (Piece == ROOK)
- b = attacks_bb<ROOK>(s, pos.occupied_squares() & ~pos.pieces(ROOK, QUEEN, Us));
+ b = attacks_bb<ROOK>(s, pos.pieces() ^ pos.pieces(ROOK, QUEEN, Us));
else
assert(false);
if ( (Piece == BISHOP || Piece == ROOK || Piece == QUEEN)
&& (PseudoAttacks[Piece][pos.king_square(Them)] & s))
{
- b = BetweenBB[s][pos.king_square(Them)] & pos.occupied_squares();
+ b = BetweenBB[s][pos.king_square(Them)] & pos.pieces();
assert(b);
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;
+
// Enemy pieces not defended by a pawn and under our attack
Bitboard weakEnemies = pos.pieces(Them)
& ~ei.attackedBy[Them][PAWN]
& ei.attackedBy[Us][0];
if (!weakEnemies)
- return SCORE_ZERO;
+ return score;
// Add bonus according to type of attacked enemy piece and to the
// type of attacking piece, from knights to queens. Kings are not
// Opponent king cannot block because path is defended and position
// is not in check. So only friendly pieces can be blockers.
assert(!pos.in_check());
- assert((queeningPath & pos.occupied_squares()) == (queeningPath & pos.pieces(c)));
+ assert((queeningPath & pos.pieces()) == (queeningPath & pos.pieces(c)));
// Add moves needed to free the path from friendly pieces and retest condition
movesToGo += popcount<Max15>(queeningPath & pos.pieces(c));