public static function str_split($str, $split_len = 1)
    {
        if (! preg_match('/^[0-9]+$/', $split_len) || $split_len < 1) {
            return false;
        }

        $len = AnHelperString::strlen($str);
        if ($len <= $split_len) {
            return array($str);
        }

        preg_match_all('/.{'.$split_len.'}|[^\x00]{1,'.$split_len.'}$/us', $str, $ar);
        return $ar[0];
    }