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]sum_temp;
assign sum_temp = {1'b0,a} + {1'b0,~b} + 5'b1;
assign diff = sum_temp[3:0];
assign bout = ~sum_temp[4];
endmodule