Picqer\Barcode\BarcodeGenerator::checksum_code93 PHP Метод

    protected function checksum_code93($code)
    {
        $chars = array('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '-', '.', ' ', '$', '/', '+', '%', '<', '=', '>', '?');
        // translate special characters
        $code = strtr($code, chr(128) . chr(131) . chr(129) . chr(130), '<=>?');
        $len = strlen($code);
        // calculate check digit C
        $p = 1;
        $check = 0;
        for ($i = $len - 1; $i >= 0; --$i) {
            $k = array_keys($chars, $code[$i]);
            $check += $k[0] * $p;
            ++$p;
            if ($p > 20) {
                $p = 1;
            }
        }
        $check %= 47;
        $c = $chars[$check];
        $code .= $c;
        // calculate check digit K
        $p = 1;
        $check = 0;
        for ($i = $len; $i >= 0; --$i) {
            $k = array_keys($chars, $code[$i]);
            $check += $k[0] * $p;
            ++$p;
            if ($p > 15) {
                $p = 1;
            }
        }
        $check %= 47;
        $k = $chars[$check];
        $checksum = $c . $k;
        // resto respecial characters
        $checksum = strtr($checksum, '<=>?', chr(128) . chr(131) . chr(129) . chr(130));
        return $checksum;
    }