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