Simple code for php to generate short URL

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

 public static 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 < $length; $i++){
   $number = bcadd($number, bcmul($baselist[$encode[$i]],  bcpow(62, $length - $i - 1)));
  }
  return $number;
 }
}