Check and clear the function of bom in php file

/**
Function: Detect and clear BOM
link: bbs.it-home.org
*/
if(isset($_GET['dir'])){
$basedir=$_GET['dir'];
}else{
$basedir = '.';
}
$auto = 1;
checkdir($basedir);
function checkdir($basedir){
  if($dh = opendir($basedir)){
  while(($file = readdir($dh)) !== false){
  if($file != '.' && $file != '..'){
     if(!is_dir($basedir."/".$file)){
       echo "filename: $basedir/$file ".checkBOM("$basedir/$file")." ";
     }else{
        $dirname = $basedir."/".$file;
        checkdir($dirname);
     }
}
}//end while
closedir($dh);
}//end if($dh
}//end function
function checkBOM($filename){
   global $auto;
   $contents = file_get_contents($filename);
   $charset[1] = substr($contents, 0, 1);
   $charset[2] = substr($contents, 1, 1);
   $charset[3] = substr($contents, 2, 1);
   if(ord($charset[1]) == 239 && ord($charset[2]) == 187 && ord($charset[3]) == 191){
      if($auto == 1){
        $rest = substr($contents, 3);
        rewrite ($filename, $rest);
        return "BOM found, automatically removed.";
      }else{
         return ("BOM found.");
      }
   }
else return ("BOM Not Found.");
}
function rewrite($filename, $data){
   $filenum = fopen($filename, "w");
   flock($filenum, LOCK_EX);
   fwrite($filenum, $data);
   fclose($filenum);
}
?>