public function bytes($bytes, $decimals = 2, $mod = 1024)
    {
        $factor = floor((strlen($bytes) - 1) / 3);
        $byte_name = $this->units_of_bytes[$factor];
        if ($mod == 1000) {
            $byte_name = str_replace('B', 'bit', $byte_name);
        }

        return sprintf("%.{$decimals}f %s", $bytes / pow($mod, $factor), $byte_name);
    }