verilog function功能函数写法

  function [15:0] sm2tc;
    input [15:0]  din;
    reg   [15:0]  dp;
    reg   [15:0]  dn;
    reg   [15:0]  dout;
    begin
      dp = {1'b0, din[14:0]};
      dn = ~dp + 1'b1;
      dout = (din[15] == 1'b1) ? dn : dp;
      sm2tc = dout;
    end
  endfunction