verilog function功能函数写法

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