alu.vhd

关于C++编程方向的一些经验

-- alu.vhd

-- This module implements a 16-bit ALU

-- Inputs: 
--    A, B     - 16-bit inputs 
--    ALUop    - 4-bit Select for ALU operation

-- Outputs: 
--    Result   - 16-bit result output
--    Zero     - 1-bit zero result output

-- Author:    Easyright
-- E-mail:    [e-mail]
-- Date:      17-08-2003
-- Copyright: http://www.EasyRight.net

------------------------------------------------------------------------------------------------------ 

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

entity alu is
  port (
    A, B:     in std_logic_vector(15 downto 0);
    ALUop:    in std_logic_vector(3 downto 0);
    Result:   out std_logic_vector(15 downto 0);
    Zero:     out std_logic
  );
end alu;

architecture arc_alu of alu is

  Signal res: std_logic_vector(15 downto 0);

  function btobv(b: boolean) return bit_vector is
  begin
    if b then
      return "0000000000000001";
    else
      return "0000000000000000";
    end if;
  end function btobv;

begin
  with ALUop select 
    res <= A + B when "0011",
           A + (not B) + 1 when "0001",
           not A when "0111",
           A and B when "0000",
           A or B when "0010",
           To_StdLogicVector(To_bitvector(A, '0') srl CONV_INTEGER(B+B)) when "0100",
           To_StdLogicVector(To_bitvector(A, '0') sra CONV_INTEGER(B+B)) when "0101",
           To_StdLogicVector(To_bitvector(A, '0') sla CONV_INTEGER(B+B)) when "0110",
           To_StdLogicVector(btobv(A < B)) when "1100",
           To_StdLogicVector(btobv(A > B)) when "1001",
           To_StdLogicVector(btobv(A <= B)) when "1110",
           To_StdLogicVector(btobv(A >= B)) when "1011",
           To_StdLogicVector(btobv(A = B)) when "1010",
           To_StdLogicVector(btobv(A /= B)) when "1101",
           "0000000000000000" when others;

  Result <= res;
  Zero <= not(res(0) or res(1) or res(2) or res(3) or res(4) or res(5) or res(6) or res(7) or 
              res(8) or res(9) or res(10) or res(11) or res(12) or res(13) or res(14) or res(15));
end arc_alu;