Swift_Mime_ContentEncoder_NativeQpContentEncoder::_standardize PHP Method

    protected function _standardize($string)
    {
        // transform CR or LF to CRLF
        $string = preg_replace('~=0D(?!=0A)|(?<!=0D)=0A~', '=0D=0A', $string);
        // transform =0D=0A to CRLF
        $string = str_replace(array("\t=0D=0A", ' =0D=0A', '=0D=0A'), array("=09\r\n", "=20\r\n", "\r\n"), $string);
        switch ($end = ord(substr($string, -1))) {
            case 0x9:
                $string = substr_replace($string, '=09', -1);
                break;
            case 0x20:
                $string = substr_replace($string, '=20', -1);
                break;
        }
        return $string;
    }