短い URL を生成するための PHP の簡単なコード

/*
* php短网址生成
* edit: bbs.it-home.org
*/
class Base62{
 private static $base62 = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNO PQRSTUVWXYZ';

 パブリック静的function encode($number, $encode = ''){
 while($number > 0){
 $mod = bcmod($number, 62);
 $encode .= self::$base62[$mod];
 $number = bcdiv(bcsub($number, $mod), 62);

 }
 return strrev($encode);
 }

 public static function decode($encode, $number = 0){
 $length = strlen($encode);
 $baselist = array_flip(str_split(self::$base62));
 for($i = 0; $i  $number = bcadd($number , bcmul($baselist[$encode[$i]], bcpow(62, $length - $i - 1)));
 }
 return $number;
 }
}