71. Arithmetic Logic Unit

How do you plan to solve it?

/*Write your code here*/
module alu4(
  input [3:0]a,b,
  input [2:0]op,
  output reg[3:0]y,
  output reg cf);

  localparam [2:0]
      ADD = 3'b000,
      SUB = 3'b001,
      AND = 3'b010,
      OR = 3'b011,
      XOR = 3'b100;

  wire [4:0] add={1'b0,a}+{1'b0,b};
  wire [4:0] sub={1'b0,a}+{1'b0,~b}+5'b1; 

  always @*
    begin
       y=4'b0000;
       cf=1'b0;
      case(op)
     
         ADD : begin
                 y=add[3:0];
                 cf=add[4];
               end  

         SUB :begin
                 y=sub[3:0];
                 cf=~(sub[4]);
              end        
         AND : y=a&b;
         OR : y=a|b;
         XOR : y=a^b;

         default :
         begin y=4'b0000;
               cf=1'b0;
         end
  endcase   
end
endmodule