library IEEE;
use IEEE.std_logic_1164.all;

entity alu1bit is
   port(  i_X    : in std_logic;
          i_Y    : in std_logic;
          i_Less :  in std_logic;
          i_Cin  :  in std_logic;
          i_Op   :  in std_logic_vector(3 downto 0);
          o_Res  :  out std_logic;
          o_Cout :  out std_logic;
          o_Set  :  out std_logic);
 end alu1bit;

 architecture structure of alu1bit is


   component add_sub_wc is
     port(      A : in std_logic;
                B : in std_logic;
         carry_in : in std_logic;
         nAdd_Sub : in std_logic;
            total : out std_logic;
        carry_out : out std_logic);
    end component;

  signal XYAnd, XYOr, XYXor, XYNand, XYNor, XYAdd, XYSub, XYSet, carry_add, carry_sub, YNot, XNot : std_logic;

 begin
  --Xmux and with Ymux
  XYAnd <= i_X AND i_Y;

  --Xmux or with Ymux
  XYOr  <= i_X OR i_Y;

  --X Xor with Y
  XYXor <= i_X XOR i_Y;

  --X NAND with Y
  XYNand <= i_X NAND i_Y;

  --X NOR with Y
  XYNor <= i_X NOR i_Y;

  --Y Inverted
  YNot <= NOT i_Y;

  --X Inverted
  XNot <= NOT i_X;

  --Add X with Y
  addXY : add_sub_wc
  port map(  A          => i_X,
             B          => i_Y,
             carry_in   => i_Cin,
             nAdd_Sub    => '0',
             total      => XYAdd,
             carry_out  => carry_add);

  --Subtract X with Y
  subXY : add_sub_wc
  port map(  A          => i_X,
             B          => YNot,
             carry_in   => i_Cin,
             nAdd_Sub   => '0',
             total      => XYsub,
             carry_out  => carry_sub);


  --Select carryout value based on operation
  with i_OP select
  o_Cout <= carry_sub when  "0011",
            carry_sub when  "0111",
            carry_add when others;




  --Selecting which value we want to send to output
  with i_OP select
  o_Res <= XYAnd  when "0000", --AND
           XYOr   when "0001", --OR
           XYAdd  when "0010", --ADD
           XYSub  when "0011", --SUBTRACT
           XYNor  when "0100", --NOR
           XYXor  when "0101", --XOR
           XYNand when "0110", --NAND
           i_Less when "0111", --SET LESS THAN
           '0' when others;


 end structure;