round_up_pow2 (guint n)
{
  n = n - 1;
  n = n | (n >> 1);
  n = n | (n >> 2);
  n = n | (n >> 4);
  n = n | (n >> 8);
  n = n | (n >> 16);
  return n + 1;
}
round_up_pow2 (guint n)
{
  n = n - 1;
  n = n | (n >> 1);
  n = n | (n >> 2);
  n = n | (n >> 4);
  n = n | (n >> 8);
  n = n | (n >> 16);
  return n + 1;
}