黑科技开根号

 

int my_sqrt( float x )
{
    if ( x==0 ) return 0;
    float result = x;
    float xhalf = 0.5f*result;
    int i = *(int*)&result;
    i = 0x5f375a86-(i>>1);
    result = *(float*)&i;
    result = result*(1.5f-xhalf*result*result);
    result = result*(1.5f-xhalf*result*result);
    return 1.0f/result;
}