71. Arithmetic Logic Unit

How do you plan to solve it?

/*Write your code here*/
module alu4(
    input [3:0]a,
    input [3:0]b,
    input [2:0]op,
    output reg [3:0]y,
    output reg cf
);
always @(*) begin
case (op)
3'b000:begin
{cf,y}=a+b;
end 
3'b001:begin y=a+~b+1;
cf=(a<b); 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