整数近似开方

unsigned long sqrt(unsigned long num)
{
    unsigned int x,tmp;      //x为所求结果  
    unsigned int i=0xffffffff;    //控制循环的次数 
    x=num/2;  
    while(i--)  
    {  
        tmp = x;
        x=(x+num/x)/2;
        if(x>=tmp)
            return tmp;
    }
    return x;
}