Priority Encoder - Data flow Architecture( Using Std_match)

library IEEE;
use IEEE.STD_LOGIC_1164.all;
use IEEE.NUMERIC_STD.all;

entity pr_encdr_4_2 is
     port(
         din : in STD_LOGIC_VECTOR(3 downto 0);
         dout : out STD_LOGIC_VECTOR(1 downto 0)
         );
end pr_encdr_4_2;


architecture pr_encdr_df of pr_encdr_4_2 is
begin
 
dout <= "00" when std_match (din,"1---") else
        "01" when std_match (din,"01--") else
        "10" when std_match (din,"001-") else
        "11" when std_match (din,"0001");
 

end pr_encdr_df;