PHP Base62 encoder/decoder

base62.class.php

<?php

class Base62 {

   private $chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

   public function base62Encode(int $num): string {
      $res = '';
      do {
         $res = $this->chars[$num % 62] . $res;
         $num = (int)($num / 62);
      } while ($num);
      return $res;
   }

   public function base62Decode(string $num): int {
      $limit = strlen($num);
      $res = strpos($this->chars, $num[0]);
      for ($i = 1; $i < $limit; $i++) {
          $res = 62 * $res + strpos($this->chars, $num[$i]);
      }
      return $res;
   }

} // End class

$inst = new Base62();
var_dump($inst->base62Encode(123456)); // Result: w7e
var_dump($inst->base62Decode('w7e')); // Result: 123456