/// that the move is a legal move from the position. The return value is
/// a string containing the move in short algebraic notation.
-const string move_to_san(const Position& pos, Move m) {
+const string move_to_san(Position& pos, Move m) {
assert(pos.is_ok());
assert(move_is_ok(m));
// Position::move_is_check doesn't detect all checks (not castling moves,
// promotions and en passant captures).
StateInfo st;
- Position p(pos);
- p.do_move(m, st);
- if (p.is_check())
- san += p.is_mate()? "#" : "+";
+ pos.do_move(m, st);
+ if (pos.is_check())
+ san += pos.is_mate() ? "#" : "+";
+ pos.undo_move(m);
return san;
}