ako vygenerovať unikátny string

function ns10toX($dec_val)
{
 $result_chars = "";
 $division = 1;
 //$chars = array("|"); //jednotkova sustava
 //$chars = array("0","1"); // dvojkova
 $chars = array("0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"); // sestnastkova, atd
 $ns = count($chars);
 $i=0;
 
 // ak sa jedna o jednotkovu sustavu
 if($ns==1)
 {
  for($i=0;$i<$dec_val;$i++)
  {
   $result_chars.=$chars[0];
  }
  return $result_chars;
 }
 //
 
 while($division!=0)
 {
  $dec_val = $i==0 ? $dec_val : $division;
  $division = floor($dec_val/$ns);
  $remainder = $dec_val%$ns;
  $result_chars[$i] = $chars[$remainder];

  $i++;
 }

 $result_chars = strrev(implode("",$result_chars));
 return $result_chars;
}