/// Fast version of move_is_legal() that takes a position a move and a
/// bitboard of pinned pieces as input, and tests whether the move is legal.
-/// This version must only be used when the side to move is not in check.
bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
assert(pos.is_ok());
- assert(!pos.is_check());
assert(move_is_ok(m));
assert(pinned == pos.pinned_pieces(pos.side_to_move()));
return false;
}
// The move is pseudo-legal, check if it is also legal
- return pos.pl_move_is_legal(m, pinned);
+ return pos.is_check() ? pos.pl_move_is_evasion(m, pinned) : pos.pl_move_is_legal(m, pinned);
}
// Luckly we can handle all the other pieces in one go
- return ( bit_is_set(pos.attacks_from(pc, from), to)
- && pos.pl_move_is_legal(m, pinned)
- && !move_is_promotion(m));
+ return bit_is_set(pos.attacks_from(pc, from), to)
+ && (pos.is_check() ? pos.pl_move_is_evasion(m, pinned) : pos.pl_move_is_legal(m, pinned))
+ && !move_is_promotion(m);
}
}
+/// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
+
+bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
+{
+ assert(pos.is_check());
+
+ Color us = side_to_move();
+ Square from = move_from(m);
+ Square to = move_to(m);
+
+ // King moves and en-passant captures are verified in pl_move_is_legal()
+ if (type_of_piece_on(from) == KING || move_is_ep(m))
+ return pl_move_is_legal(m, pinned);
+
+ Bitboard target = checkers();
+ Square checksq = pop_1st_bit(&target);
+
+ if (target) // double check ?
+ return false;
+
+ // Our move must be a blocking evasion or a capture of the checking piece
+ target = squares_between(checksq, king_square(us)) | checkers();
+ return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
+}
+
+
/// Position::move_is_check() tests whether a pseudo-legal move is a check
bool Position::move_is_check(Move m) const {
// Properties of moves
bool pl_move_is_legal(Move m, Bitboard pinned) const;
+ bool pl_move_is_evasion(Move m, Bitboard pinned) const;
bool move_is_check(Move m) const;
bool move_is_check(Move m, Bitboard dcCandidates) const;
bool move_is_capture(Move m) const;