library IEEE;
use IEEE.STD_LOGIC_1164.all;
use IEEE.STD_LOGIC_UNSIGNED.all;

entity BCD_Excess is
    port( B : in std_logic_vector(3 downto 0);
            E : out std_logic_vector(3 downto 0));
end BCD_Excess;

architecture Z_case of BCD_Excess is
    --V1/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\

    --E(3)<= not((not B(3)and not B(2))or (not B(3) and not B(1) and not B(0)));
    --E(2)<=(not B(2)and B(0)) or (not B(2) and B(1)) or (B(2) and not B(1) and not B(0));
    --E(1)<=(not B(1) and not B(0)) or (B(1)and B(0));
    --E(0)<= not B(0);

    --V2/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\

    --E <= B + 3;

    --V3/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\

    --process(B)
    --begin
    --  case B is
    --      when "0000" => E <= "0011";
    --      when "0001" => E <= "0100";
    --      when "0010" => E <= "0101";
    --      when "0011" => E <= "0110";
    --      when "0100" => E <= "0111";
    --      when "0101" => E <= "1000";
    --      when "0110" => E <= "1001";
    --      when "0111" => E <= "1010";
    --      when "1000" => E <= "1011";
    --      when "1001" => E <= "1100";
    --      when others => E <= "----";
    --  end case;
    --end process;

    --V4/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\/--\
begin
    process(B)
    begin
        if B < "1010" then
            E <= B+3;
        else
            E <= "0000";
        end if;
    end process;
end Z_case;