1:  sub numtoname {
2:      local ($_) = @_;
3:      unless (defined $numtoname{$_}) {
4:          my (@a) = gethostbyaddr(pack('C4', split(/\./)),2);
5:          $numtoname{$_} = @a > 0 ? $a[0] : $_;
6:      }
7:      return $numtoname{$_};
8:  }