php把全角数字转为半角数字

function getalabnum($fnum) 
{ 
 $nums = array("０","１","２","３","４","５","６","７","８","９","＋","－","％","．"); 
 $fnums = "0123456789+-%."; 
 for($i=0;$i<count($nums);$i++){ 
  if($nums[$i]==$fnum) return $fnums[$i]; 
 }//开源代码phpfensi.com 
 return $fnum; 
} 
//实例应用 
echo getalabnum(&#39;６&#39;); // 6