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