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);
  always @* begin
    case(op)
    3'b000 : {cf,y} = a+b;
    3'b001 : {cf,y} = a + (~b) + 1;
    3'b010 : begin y = a & b ; cf = 1'b0; end
    3'b011 : begin y = a | b ; cf = 1'b0; end
    3'b100 : begin y = a ^ b ; cf = 1'b0; end
    default: begin y = 4'b0000; cf = 1'b0; end
    endcase
  end
endmodule