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
);
 reg [4:0] z ;
always@(*)
    begin
        case(op)
        3'b000 : begin
            z = a + b ;
            y = z[3:0];
            cf = z[4];
         end
        3'b001 : begin 
            z = a + ~b +1 ;
            y = z[3:0];
            cf = z[4];
        end 
        3'b010 : begin 
            y = a & b;
            cf =0;
         end
        3'b011 : begin 
            y = a | b ;
            cf = 0;
        end 
        3'b100 :begin 
            y = a ^ b ;
            cf = 0;
        end
        default : begin y = 4'b0000; cf = 0; end
        endcase
    end
endmodule