#include <string>
#include <iostream>

using namespace std;

uint16_t crcAdd(uint8_t c) {
    int crc = 0;

    for (int j = 0; j < 8; j++) {
        if ( (crc ^ c) & 0x0001 ) {
            crc = (crc >> 1) ^ 0xA001;
        } else {
            crc = crc >> 1;
        }

        c = c >> 1;
    }
    return crc;
}

uint16_t update_crc_16( uint16_t crc, unsigned char c ) {
	return (crc >> 8) ^ crcAdd((crc ^ (uint16_t) c) & 0x00FF);
}

class Reliable {
public:
    uint16_t getCrc() {
        return crc;
    }

    uint16_t* getCrcAddr() {
        return &crc;
    }

protected:
    virtual uint16_t calculateCrc() = 0;

    void updateCrc(int crc) {
        this->crc = crc;
    }

    void assertCorrectCrc() {
        assert(calculateCrc() == getCrc());
    }

private:
    uint16_t crc;
};

class ReliableInt: public Reliable {
public:
    ReliableInt(int value) : value(value) {
        updateCrc(calculateCrc());
    }

    ReliableInt operator + (ReliableInt other) {
        this->assertCorrectCrc();
        other.assertCorrectCrc();
        return ReliableInt(value + other.value);
    }

    ReliableInt operator - (ReliableInt other) {
        this->assertCorrectCrc();
        other.assertCorrectCrc();
        return ReliableInt(value - other.value);
    }

private:
    uint16_t calculateCrc() override {
        uint16_t crc = 0;
        int copyval = value;
        for (int i = 0; i < 4; i++) {
            crc = update_crc_16(crc, (uint8_t)copyval & 0xFF);
            copyval >>= 4;
        }
        return crc;
    }

    int value;
};

class ReliableString: public Reliable {
public:
    ReliableString(const string& value) : value(value) {
        updateCrc(calculateCrc());
    }
private:
    uint16_t calculateCrc() override {
        uint16_t crc = 0;
        for (char c : value) {
            crc = update_crc_16(crc, (uint8_t)c);
        }
        return crc;
    }

    string value;
};

int main() {
    ReliableInt a(5);
    ReliableInt b(10);

    cout << a.getCrc() << ' ' << b.getCrc() << endl;
    cout << (a + b).getCrc() << endl;

    // Destroy CRC value of A
    uint16_t* addr = a.getCrcAddr();
    ++(*addr);

    cout << (a + b).getCrc() << endl;

    return 0;
}