实测double在$10^{-8}$的精度时出现误差！

#include <bits/stdc++.h>
using namespace std;
double sqrt_(double num){
	const double eps = 1e-8;
	double L = 0.0,R = num;
	double mid = (R+L)/2.0;
	while((R-L)>eps){
		if(mid*mid>num){
			R = mid;
		}else{
			L = mid;
		}
		mid = (R+L)/2.0;
	}
	return mid;
}
int main() {
	printf("%.8lf\n",sqrt_(7.0)*sqrt_(7.0));
	return 0;
}