69. Binary Subtractor

How do you plan to solve it?

/*Write your code here*/
module sub4_2c(
    input [3:0] a,
    input [3:0] b,
    output [3:0] diff,
    output bout
);
wire [4:0] temp;

assign temp = a+(~b) +1;
assign bout = temp[4];
assign diff = temp[3:0];

endmodule