- // After castling, the rook and king's final positions are exactly the same
- // in Chess960 as they would be in standard chess.
- Square kfrom = pos.king_square(us);
- Square rfrom = pos.castle_rook_square(f);
- Square kto = relative_square(us, Side == KING_SIDE ? SQ_G1 : SQ_C1);
- Square rto = relative_square(us, Side == KING_SIDE ? SQ_F1 : SQ_D1);
-
- assert(!pos.in_check());
- assert(pos.piece_on(kfrom) == make_piece(us, KING));
- assert(pos.piece_on(rfrom) == make_piece(us, ROOK));
-
- // Unimpeded rule: All the squares between the king's initial and final squares
- // (including the final square), and all the squares between the rook's initial
- // and final squares (including the final square), must be vacant except for
- // the king and castling rook.
- for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); s++)
- if ( (s != kfrom && s != rfrom && !pos.square_is_empty(s))
- ||(pos.attackers_to(s) & pos.pieces(them)))
- return mlist;
-
- for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); s++)
- if (s != kfrom && s != rfrom && !pos.square_is_empty(s))
- return mlist;
+ // Generate blocking evasions or captures of the checking piece
+ Square checksq = lsb(pos.checkers());
+ Bitboard target = between_bb(checksq, ksq) | checksq;