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] sum5 = {1'b0, a} + {1'b0, ~b} + 5'b00001;
    assign diff = sum5[3:0];
    assign bout = ~sum5[4];
endmodule