library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;
 
entity alu is
	Port (	inp_a : in signed(3 downto 0);
		inp_b : in signed(3 downto 0);

		--- sel = M S3 S2 S1 S0 */
		sel : in STD_LOGIC_VECTOR (3 downto 0);

		carry_in : in std_logic;

		--- carry_out O3 O2 O1 O0 */
		out_alu_tmp : buffer signed(4 downto 0);
		out_alu : out signed(4 downto 0);

		--- fast carry */
		p : out std_logic; --- propagate */ 
		g : out std_logic --- generate */
		);
end alu;
 
architecture Behavioral of alu is
begin
process(inp_a, inp_b, sel)
begin

--- ACTIVE HIGH DATA */
--- sel = M S3 S2 S1 S0 */
case sel is
	--- LOGIC */
	when "00000" =>
	out_alu <= not inp_a;
	when "00001" =>
	out_alu <= not (inp_a or inp_b);
	when "00010" =>
	out_alu <= (not inp_a) and inp_b;
	when "00011" =>
	out_alu <= "0000";

	when "00100" =>
	out_alu <= not (inp_a and inp_b);
	when "00101" =>
	out_alu <= not(inp_b);
	when "00110" =>
	out_alu <= inp_a xor inp_b;
	when "00111" =>
	out_alu <= inp_a and not(inp_b);

	when "01000" =>
	out_alu <= not(inp_a) + inp_b;
	when "01001" =>
	out_alu <= not(inp_a xor inp_b);
	when "01010" =>
	out_alu <= inp_b; when "01011" =>
	out_alu <= inp_a and inp_b;

	when "01100" =>
	out_alu <= "1111";
	when "01101" =>
	out_alu <= inp_a or not(inp_b);
	when "01110" =>
	out_alu <= inp_a or inp_b;
	when "01111" =>
	out_alu <= inp_a;

	--- ARITHMETIC - M=0*/
	--- assuming carry_in is low */
	when "10000" =>
	out_alu <= inp_a;
	when "10001" =>
	out_alu <= inp_a or inp_b;
	when "10010" =>
	out_alu <= inp_a or not(inp_b);
	when "10011" =>
	out_alu <= "1111"; --- -1, 2sCompl*/

	when "10100" =>
	out_alu <= inp_a + (inp_a and not(inp_b));
	when "10101" =>
	out_alu <= (inp_a or inp_b) + (inp_a and not(inp_b));
	when "10110" =>
	out_alu <= inp_a - inp_b - 1;
	when "10111" =>
	out_alu <= (inp_a and not(inp_b)) - 1;

	when "11000" =>
	out_alu <= inp_a + (inp_a and inp_b);
	when "11001" =>
	out_alu <= inp_a + inp_b;
	when "11010" =>
	out_alu <= (inp_a or not(inp_b)) + (inp_a and inp_b);
	when "11011" =>
	out_alu <= (inp_a and inp_b) - 1;

	when "11100" =>
	out_alu <= (inp_a + (inp_a sll 1)); -- A plus shited_A */
	when "11101" =>
	out_alu <= (inp_a or inp_b) + inp_a;
	when "11110" =>
	out_alu <= (inp_a or not(inp_b)) + inp_a;
	when "11111" =>
	out_alu <= inp_a - 1;

	when others =>
	NULL;
end case;

--- add potential carry_in */
if carry_in = '1' then
	out_alu <= out_alu_tmp + 1;
end if;

p <= inp_a or inp_b;
g <= inp_a and inp_b;

end process;
 
end Behavioral;