php 生成短URL的算法

function code62($x){
$show='';
while($x>0){
$s=$x % 62;
if ($s>35){
$s=chr($s+61);
}elseif($s>9&&$s<=35){
$s=chr($s+55);
}
$show.=$s;
$x=floor($x/62);
}
return $show;
}
function shorturl($url){
$url=crc32($url);
$result=sprintf("%u",$url);
return code62($result);
}