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
    cf=1'b0;
case(op)
3'b000:{cf,y}=a+b;
3'b001: {cf,y}=a+~b+1;
3'b010: y=a&b;
3'b011:y=a|b;
3'b100:y=a^b;
default: begin
    y=4'd0;
    cf=1'b0;
end
endcase
end
endmodule