Core_Email::_prep_q_encoding

protected function _prep_q_encoding($str, $from = false)
{
    $str = str_replace(array("\r", "\n"), array('', ''), $str);

    // Line length must not exceed 76 characters, so we adjust for
    // a space, 7 extra characters =??Q??=, and the charset that we will add to each line
    $limit = 75 - 7 - strlen($this->charset);

    // these special characters must be converted too
    $convert = array('_', '=', '?');

    if ($from === true)
    {
        $convert[] = ',';
        $convert[] = ';';
    }

    $output = '';
    $temp = '';

    for ($i = 0, $length = strlen($str); $i < $length; $i++)
    {
        // Grab the next character
        $char = $str[$i];
        $ascii = ord($char);

        // convert ALL non-printable ASCII characters and our specials
        if ($ascii < 32 || $ascii > 126 || in_array($char, $convert))
        {
            $char = '='.dechex($ascii);
        }

        // handle regular spaces a bit more compactly than =20
        if ($ascii === 32)
        {
            $char = '_';
        }

        // If we're at the character limit, add the line to the output,
        // reset our temp variable, and keep on chuggin'
        if ((strlen($temp) + strlen($char)) >= $limit)
        {
            $output .= $temp.$this->crlf;
            $temp = '';
        }

        // Add the character to our temporary line
        $temp .= $char;
    }

    // wrap each line with the shebang, charset, and transfer encoding
    // the preceding space on successive lines is required for header "folding"
    return trim(preg_replace('/^(.*)$/m', ' =?'.$this->charset.'?Q?$1?=', $output.$temp));
}