main.cpp

//compile using g++  -std=c++17 main.cpp uuid.cpp  -luuid  -o utest -O3

#include "uuid.hpp"
#include <iostream>

using namespace horizon;

int main(void) {
	UUID r;

	std::cout << r.hash() << std::endl;
	for(int i = 0; i< 1; i++) {
		std::cout << r.hash() << std::endl;
	}
	
	return 0;
}

uuid.cpp

#include "uuid.hpp"
#include <cstring>

namespace horizon {

UUID::UUID()
{
    memset(uu, 0, sizeof(uu));
    uu[15] = 0xff;
}

}; // namespace horizon

uuid.hpp

#pragma once
#include <cstddef>


namespace horizon {
class UUID {
public:
    UUID();

    size_t hash() const
    {
        size_t r = 0;
        for (size_t i = 0; i < 16; i++) {
            r ^= uu[i] << ((i % sizeof(size_t)) * 8);
        }
        return r;
    }

private:
    unsigned char uu[16];
};
} // namespace horizon