快速求平方根

float mySqrt(float x)
{
float a = x;
unsigned int i = *(unsigned int *)&x;
i = (i + 0x3f76cf62) >> 1;
x = *(float *)&i;
x = (x + a / x) * 0.5;
return x;
}
误差千分之6

参考网址：
https://blog.csdn.net/xtlisk/article/details/51249371