计算两点间的距离+浮点数按精度四舍五入

// 返回x的平方根的倒数，很诡异的算法
float InvSqrt(float f32Num)
{
    float f32Half = 0.5f * f32Num;
    int i32Num = *(int*) &f32Num; // store floating-point bits in integer
    
    i32Num = 0x5f3759d5 - (i32Num >> 1); // initial guess for Newton's method
    f32Num = *(float*) &i32Num; // convert new bits into float
    f32Num = f32Num * (1.5f - f32Half * f32Num * f32Num); // One round of Newton's method

    return f32Num;
}

struct Point
{
    int i32PixelX;
    int i32PixelY;

    Point(int i32PixelX, int i32PixelY)
    {
        this->i32PixelX = i32PixelX;
        this->i32PixelY = i32PixelY;
    }
};

// 求两点间的距离
float Distance(Point* pstPoint1, Point* pstPoint2)
{
    int i32XDist = pstPoint1->i32PixelX - pstPoint2->i32PixelX;
    int i32YDist = pstPoint1->i32PixelY - pstPoint2->i32PixelY;
    float f32Num = (float) (i32XDist * i32XDist + i32YDist * i32YDist);

    return InvSqrt(f32Num) * f32Num;
}

// 浮点数四舍五入，默认保留3位小数
float FloatRound(float f32Num, int i32Precision/* = 3*/)
{
    int i32Multiple = 1;
    for (int i = 0; i < i32Precision; i++)
    {
        i32Multiple *= 10;
    }

    if (f32Num > 0)
    {
        return (int)((f32Num * i32Multiple) + 0.5) / (float)i32Multiple;
    }
    else
    {
        f32Num = -f32Num;
        return -((int)((f32Num * i32Multiple) + 0.5) / (float)i32Multiple);
    }
}

int main(int argc, char* argv[])
{
    float f32Value = 4;
    float f32InvSqrt = InvSqrt(f32Value);
    float f32Sqrt = f32InvSqrt * f32Value;

    Point stPoint1(3, 0);
    Point stPoint2(0, 4);

    float f32Dist = Distance(&stPoint1, &stPoint2);
    printf("%f, %f, %f\n", f32InvSqrt, f32Sqrt, f32Dist);

    float f1 = FloatRound((float)0.2544, 3);
    float f2 = FloatRound(0.2545, 3);
    if (f1 < f2)
    {
        printf("ok\n");
    }

    return 0;
}