function Check($username, $password) {
   		if ($state = $mysqli->prepare("SELECT username, password FROM table-utenti WHERE username = ? LIMIT 1")) {
      	$state->bind_param('s', $username);
      	$state->execute();
      	$state->store_result();
      	$state->bind_result($db_username, $db_password, $db_nome);
      	$state->fetch();
      	$password = hash('sha512', $password);
      		if($state->num_rows == 1) {

         		if($db_password == $password) {
            	// Password corretta!

         		}

      		}
		}