cek CRC

public static boolean isQRISValid(String qrdata) {
        //checsum 4 digit ascii
        if (qrdata != null && qrdata.length() > 4) {
            String qrDataNonCRC = qrdata.substring(0, qrdata.length() - 4);
            String qrCRC = qrdata.substring(qrdata.length()-4).toUpperCase();

            if (qrDataNonCRC.startsWith("00") && qrCRC.equals(checkCRC(qrDataNonCRC.getBytes()))) {
                return true;
            }
        }
        return false;
    }

    public static String checkCRC(byte []bytes) {
        int crc = 0xFFFF;
        int polynomial = 0x1021;
        String sCRC = "";

        for (byte b : bytes) {
            for (int i = 0; i < 8; i++) {
                boolean bit = ((b   >> (7-i) & 1) == 1);
                boolean c15 = ((crc >> 15    & 1) == 1);
                crc <<= 1;
                if (c15 ^ bit) crc ^= polynomial;
            }
        }
        crc &= 0xffff;

        sCRC = Integer.toHexString(crc).toUpperCase();
        System.out.println("CRC16-CCITT = " + sCRC);
        return sCRC;
    }