A simple script to calculate the floor(sqrt(x)) with binary search in cpp. Also prevents the integer overflow on large values.

floor_sqrt.cpp

unsigned long long floor_sqrt(unsigned long long x)
{
	unsigned long long low = 0, high = x;
	// prevent integer overflow on pow2
	if (high > 18446744065119617025)
		return 4294967296;
	if (high > 4294967296 * 2 - 1)
		high = 4294967296 * 2 - 1;
	// use binary search
	while(low <= high)
	{
		const auto mid = (low + high) / 2;
		const auto pow2 = mid * mid;
		if (pow2 == x)
			return mid;
		
		if (pow2 < x) // target must be higher
			low = mid + 1;
		else // target must be lower
			high = mid - 1;
	}
	return high; // this returns the floor of the sqrt
}