开方

include<iostream>
#include<cmath>
using namespace std;
 
float InvSqrt(float x)
{
	float xhalf = 0.5f*x;
    int i = *(int*)&x; // get bits for floating VALUE 
    //i = 0x5f375a86- (i>>1); // gives initial guess y0
    i/=2;
	i = 1597463174- i;
	x = *(float*)&i; // convert bits BACK to float
    x = x*(1.5f-xhalf*x*x); // Newton step, repeating increases accuracy
    x = x*(1.5f-xhalf*x*x); // Newton step, repeating increases accuracy
    x = x*(1.5f-xhalf*x*x); // Newton step, repeating increases accuracy
 
    return 1/x;
}