Subversion Repositories mips_fault_tolerant

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-- Company: 

-- Engineer: 

-- 

-- Create Date:    01:51:49 04/11/2012 

-- Design Name: 

-- Module Name:    adder - Behavioral 

-- Project Name: 

-- Target Devices: 

-- Tool versions: 

-- Description: 

--

-- Dependencies: 

--

-- Revision: 

-- Revision 0.01 - File Created

-- Additional Comments: 

--

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library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

--use IEEE.STD_LOGIC_ARITH.ALL;

-- Uncomment the following library declaration if using

-- arithmetic functions with Signed or Unsigned values

use IEEE.NUMERIC_STD.ALL;

-- Uncomment the following library declaration if instantiating

-- any Xilinx primitives in this code.

--library UNISIM;

--use UNISIM.VComponents.all;

entity adder is

Port

(

           A : in  STD_LOGIC_VECTOR (31 downto 0);

           B : in  STD_LOGIC_VECTOR (31 downto 0);

           ALUop : in  STD_LOGIC_VECTOR (1 downto 0);

                          --ov : out std_logic;

                          S : out  STD_LOGIC_VECTOR (31 downto 0)

);

end adder;

architecture Behavioral of adder is

begin

adder:process(ALUop,A,B)

variable  add_sub : STD_LOGIC_VECTOR (32 downto 0);

variable  ov_temp : STD_LOGIC;

--variable  A_sn,B_sn,result :  signed(31 downto 0);

--variable  A_i,B_i :integer; 

         begin

         CASE ALUop IS

              When  "00"  =>

                                                add_sub := (A(31) & A) + (B(31) & B);

                                                                ov_temp := (A(31) and B(31) and (not add_sub(31))) or

                                                                ((not A(31)) and (not B(31)) and add_sub(31));

                                                                --ov <= ov_temp;

                        When  "01"  =>

                                                                add_sub := ('0' & A) + ('0' & B);

                                                                ov_temp := add_sub(32);

                        When  "10"  =>

                                       add_sub := (A(31) & A) - (B(31) & B);

                                                                ov_temp := ((not A(31)) and B(31) and add_sub(31)) or

                                                                (A(31) and (not B(31)) and (add_sub(31)));

                                                                --ov <= ov_temp;

                        When  "11"  =>

                                                                add_sub := ('0' & A) - ('0' & B);

                                                                ov_temp := add_sub(32);

         When others =>

                                        S <= (others =>'0');

         end Case;

             S <= add_sub(31 downto 0);

                       end process adder;

end Behavioral;