69. Binary Subtractor

How do you plan to solve it?

/*Write your code here*/
module sub4_2c(
input [3:0] a, b,
output [3:0] diff,
output bout
);
wire [4:0] sum = {1'b0, a}+ {1'b0, ~b}+5'b00001;
assign diff = sum[3:0];
assign bout = ~sum[4];
endmodule