-- converts a character into a std_logic

function to_std_logic(c: character) return std_logic is 
    variable sl: std_logic;
    begin
      case c is
        when 'U' => 
           sl := 'U'; 
        when 'X' =>
           sl := 'X';
        when '0' => 
           sl := '0';
        when '1' => 
           sl := '1';
        when 'Z' => 
           sl := 'Z';
        when 'W' => 
           sl := 'W';
        when 'L' => 
           sl := 'L';
        when 'H' => 
           sl := 'H';
        when '-' => 
           sl := '-';
        when others =>
           sl := 'X'; 
    end case;
   return sl;
  end to_std_logic;


-- converts a string into std_logic_vector

function to_std_logic_vector(s: string) return std_logic_vector is 
  variable slv: std_logic_vector(s'high-s'low downto 0);
  variable k: integer;
begin
   k := s'high-s'low;
  for i in s'range loop
     slv(k) := to_std_logic(s(i));
     k      := k - 1;
  end loop;
  return slv;
end to_std_logic_vector;