library  ieee;	
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity multiple_4 is
	port (a,b:in std_logic_vector(3 downto 0);
			y:out std_logic_vector(7 downto 0));
end multiple_4;

architecture behave of multiple_4 is
signal s0,s1,s2,s3:std_logic_vector(3 downto 0);
begin
	process(a,b,s0,s1,s2,s3)
	begin
		if b(0)='0'then s0<="0000";
		else s0<=a;
		end if;
		if b(1)='0'then s1<="0000";
		else s1<=a;
		end if;
		if b(2)='0'then s2<="0000";
		else s2<=a;
		end if;
		if b(3)='0'then s3<="0000";
		else s3<=a;
		end if;
	y<=("0000"&s0)+("000"&s1&'0')+("00"&s2&"00")+('0'&s3&"000");
	end process;
end behave;

library  ieee;	
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity multip_4 is
	port (a,b:in std_logic_vector(3 downto 0);
			y:out std_logic_vector(7 downto 0));
end multip_4;

architecture behave of multip_4 is
signal s1:std_logic_vector(3 downto 0);
signal s2:std_logic_vector(4 downto 0);
signal s3:std_logic_vector(5 downto 0);
signal s4:std_logic_vector(6 downto 0);
begin
	s1<=a when b(0)='1' else "0000";
	s2<=(a&'0')when b(1)='1'else"00000";
	s3<=(a&"00")when b(2)='1'else"000000";
	s4<=(a&"000")when b(3)='1'else"0000000";
	y<=s1+s2+s3+('0'&s4);
end behave;