快速质数判断

bool checkSix(const int num) {
	unsigned int i, half;
	if (num <= 1)
		return 0;
	if (num == 2 || num == 3)
		return 1;
	else if (num % 6 != 1 && num % 6 != 5)
		return 0;	
	half = (unsigned int)sqrt(num);
	for (i = 5; i <= half; i += 6) {
		if (num % i == 0 || num % (i + 2) == 0)
			return 0;
	}
	return 1;
}