code: public function decode($value, $b = 62)
      {
          $limit = strlen($value);
          $result = strpos($this->base, $value[0]);
  
          for ($i = 1; $i < $limit; $i++) {
              $result = $b * $result + strpos($this->base, $value[$i]);
          }
  
          return $result;
      }
docs: Decode a string to a integer.
  
  @param string $value
  @param int $b
  
  @return int