快速开根模板（卡马克算法）

精度不是很高  代码如下

float SqrtByCarmack( float number )
{
    int i;
    float x2, y;
    const float threehalfs = 1.5F;

    x2 = number * 0.5F;
    y  = number;
    i  = * ( int * ) &y;
    i  = 0x5f375a86 - ( i >> 1 );
    y  = * ( float * ) &i;
    y  = y * ( threehalfs - ( x2 * y * y ) );
    y  = y * ( threehalfs - ( x2 * y * y ) );
    y  = y * ( threehalfs - ( x2 * y * y ) );
    return number*y;
}