sub round
{
  my $zahl=shift;
  return undef unless(defined($zahl));
  my $stelle=shift || 0;
  
  # prepare for Xe[+-]Y Notation
  # handle big float
  my ($pre,$number,$exponent)=$zahl=~/^([-+]?)(\d+\.?\d*)(?:e([+-]?\d+))?$/;
  $exponent=0 unless defined($exponent);
  $pre='' if(!$pre || $pre ne '-');
  
  # full integer zz with exponent
  my ($l)=$number=~/\.(.+)$/;
  $l=$l?length($l):0;
  $exponent-=$l;
  $number=~y/.//d;

  # correct position for round
  my $stellen=$stelle+$exponent;
  if($stellen<0)
  {
    $exponent=-$stelle;
    my $add=substr(('0'x abs($stellen)).sprintf("%.0f",$number),$stellen,-$stellen);

    # round...
    $number+=$add;

    $number=('0'x abs($stellen)).sprintf("%.0f",$number);
    substr($number,$stellen,-$stellen,'');
  }
  
  # reconstruct number
  $zahl="$pre${number}e$exponent";
  return $zahl+0;
}