module alu(clock,reset,a, b, sum[3:0], sum[4]);
   input clock, reset;
   input [3:0]  a;
   input [3:0]  b;
   output [4:0]	sum;

   wire [4:0] 	sum;


   // this ALU only support + operation
    assign {sum} = funcalu(a,b);
    function [4:0] funcalu;
      input [4:0] a;
      input [4:0] b;
 	funcalu = a[3:0]+b[3:0];
    endfunction // funcalu

endmodule // alu