int compare_route_entries(const void *a, const void *b)
{
 const struct route_table_entry *entry_a = (const struct route_table_entry *)a;
 const struct route_table_entry *entry_b = (const struct route_table_entry *)b;

 if (entry_a->prefix == entry_b->prefix)
 {
  if (entry_a->mask == entry_b->mask)
  {
   return 0;
  }
  else
  {
   if (entry_a->mask > entry_b->mask)
    return 1;
   else
    return -1;
  }
 }
 else
 {
  if (entry_a->prefix > entry_b->prefix)
   return 1;
  else
   return -1;
 }
}




struct route_table_entry *best_route(struct route_table_entry *route_table, int rt_len, uint32_t ip)
{
 int left = 0, right = rt_len - 1;
 struct route_table_entry *best = NULL;
 while (left <= right)
 {
  int mid = left + (right - left) / 2;
  struct route_table_entry *rt = &route;_table[mid];
  if ((rt->mask & ip) == (rt->mask & rt->prefix))
  {
   if (best == NULL || rt->mask > best->mask)
   {
    best = rt;
   }
   left = mid + 1;
  }
  else
  {
   right = mid - 1;
  }
 }
 return best;
}