public function addHashPrefixes($prefixes, $list)
  {
    $listdir=$this->getListStorageDir($list);
    if(!is_dir($listdir)){
      mkdir($listdir, 0777, true);
    }
    $new_prefixes=array_map('bin2hex',$prefixes);
    if(is_file($listdir.$this->prefixes_filename)){
      $existing_prefixes=explode("\n",file_get_contents($listdir.$this->prefixes_filename));
      foreach($new_prefixes as $new_prefix){
        $existing_prefixes[]=$new_prefix;
      }
      sort($existing_prefixes,SORT_STRING);
      file_put_contents($listdir.'prefixes', implode("\n",$existing_prefixes));
    }else{
      sort($new_prefixes,SORT_STRING);
      file_put_contents($listdir.'prefixes', implode("\n",$new_prefixes));
    }
    $this->debugLog('addHashPrefixes() added '.count($new_prefixes).' prefixes to list '.$list);
  }