- Square rfrom = pos.castle_rook_square(CR[us]);
- Square kto = relative_square(us, Side == KING_SIDE ? SQ_G1 : SQ_C1);
- Square rto = relative_square(us, Side == KING_SIDE ? SQ_F1 : SQ_D1);
- Bitboard enemies = pos.pieces(flip(us));
-
- 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(rfrom, rto), e = std::max(rfrom, rto); s <= e; s++)
- if (s != kfrom && s != rfrom && !pos.square_is_empty(s))
- return mlist;
-
- for (Square s = std::min(kfrom, kto), e = std::max(kfrom, kto); s <= e; s++)
- if ( (s != kfrom && s != rfrom && !pos.square_is_empty(s))
- ||(pos.attackers_to(s) & enemies))
- return mlist;
-
- // Because we generate only legal castling moves we need to verify that
- // when moving the castling rook we do not discover some hidden checker.
- // For instance an enemy queen in SQ_A1 when castling rook is in SQ_B1.
- if (pos.is_chess960())
- {
- Bitboard occ = pos.occupied_squares();
- clear_bit(&occ, rfrom);
- if (pos.attackers_to(kto, occ) & enemies)
- return mlist;
- }