php代码把全角数字转为半角数字

//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 = array('0','1', '2','3', '4','5', '6', '7','8', '9','.', '-', '+',':');
$fnlen = count($fnums);
for($i=0;$i<$fnlen;$i++) $fnum = str_replace($nums[$i],$fnums[$i],$fnum);
$slen = strlen($fnum);
$oknum = '';
for($i=0;$i<$slen;$i++){
if(ord($fnum[$i]) > 0x80) $i++;
else $oknum .= $fnum[$i];
}
if($oknum=="") $oknum=0;
return $oknum;
}