library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
 
-- Add two numbers
 
entity adder is 
  port (
    a_i:      in unsigned(3 downto 0);
    b_i:      in unsigned(3 downto 0);
    sum_o:    out unsigned(3 downto 0)
  );
end; 
 
architecture rtl of adder is 
begin
 
  add_p : process(a_i, b_i)
  begin
    sum_o <= a_i + b_i; 
  end process add_p;
 
end; -- architecture