struct ghash
{
	static std::tuple<int,int> decode(unsigned h)
	{
		const unsigned S=0x80000000;

		int x=0,y=0;
		for(int i=0;i<16;i++)
		{
			x<<=1;
			y<<=1;

			if(h&S) 
				x|=1;
			h<<=1;

			if(h&S) 
				y|=1;
			h<<=1;
		}

		return std::make_tuple(x-32768,y-32768);
	}

	static unsigned encode(int x, int y)
	{
		return encode_(x+32768,y+32768);
	}

public: //test
	static void test_code(int x,int y)
	{
		unsigned h=ghash::encode(x,y);
		auto t=ghash::decode(h);

		printf("src x=%X,y=%X hash=%X,check x=%X,y=%X\n",x,y,h,std::get<0>(t),std::get<1>(t));
	}

	static void test()
	{
		for(int i=0;i<10;i++)
		{
			test_code((4<<i)-1,(4<<i)-1);
			test_code((4<<i)-1,(4<<i));
			test_code((4<<i)-1,(4<<i)-1);
			test_code((4<<i),(4<<i)-1);
		}
	}
private:
	static unsigned encode_(unsigned short x, unsigned short y)
	{
		const unsigned S=0x8000;
		unsigned r=0;
		for(int i=0;i<16;i++)
		{
			r<<=2;
			if(x&S)
			{
				r|=(y&S)?3:2;
			}
			else
			{
				if(y&S) r|=1;
			}

			x<<=1;
			y<<=1;
		}
		
		return r;
	}
};