71. Arithmetic Logic Unit

How do you plan to solve it?

module alu4(input [3:0]a,b,
input [2:0]op,
output reg [3:0]y,
output reg cf);
always @(*)
begin
    y=1'b0;
    case(op)
    3'b000 : {cf,y}=a+b;
    3'b001 : {cf,y}=a+(~b)+1;
    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=1'b0;
        cf=0;
    end
    endcase
end
endmodule