减少冗余计算的优化对比

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优化前的代码如下所示，这是一个旋转点的函数，其中Sin(Angle),Cos(Angle)都各运算了两次，因此存在冗余计算。

通过2次优化效率有 2.2秒提升到 1.7秒，再提升到1.5秒。冗余计算优化还是非常有效果的

using System;using System.Drawing;namespace speed{    class Program    {        static void Main(string[] args)        {            int i;            Point pt = new Point(15, 78);            double angle = 45d;            DateTime dt = DateTime.Now;            for (i = 0; i < 10000000; i++)            {                RotatePt_1(angle, pt);            }            TimeSpan ts = DateTime.Now - dt;            Console.WriteLine("RotatePt_1 cost time {0}", ts.ToString());            dt = DateTime.Now;            for (i = 0; i < 10000000; i++)            {                RotatePt_2(angle, pt);            }            ts = DateTime.Now - dt;            Console.WriteLine("RotatePt_2 cost time {0}", ts.ToString());            dt = DateTime.Now;            for (i = 0; i < 10000000; i++)            {                RotatePt_3(angle, pt);            }            ts = DateTime.Now - dt;            Console.WriteLine("RotatePt_3 cost time {0}", ts.ToString());            Console.Read();        }        static Point RotatePt_1(double angle, Point pt)        {            Point pRet = new Point();            angle = -angle;            pRet.X = (int)((double)pt.X * Math.Cos(angle) - (double)pt.Y * Math.Sin(angle));            pRet.Y = (int)((double)pt.X * Math.Sin(angle) + (double)pt.Y * Math.Cos(angle));            return pRet;        }        static Point RotatePt_2(double angle, Point pt)        {            Point pRet = new Point();            angle = -angle;            double SIN_ANGLE = Math.Sin(angle);            double COS_ANGLE = Math.Cos(angle);            pRet.X = (int)(pt.X * COS_ANGLE - pt.Y * SIN_ANGLE);            pRet.Y = (int)(pt.X * SIN_ANGLE + pt.Y * COS_ANGLE);            return pRet;        }        static Point RotatePt_3(double angle, Point pt)        {            angle = -angle;            double SIN_ANGLE = Math.Sin(angle);            double COS_ANGLE = Math.Cos(angle);            return new Point((int)(pt.X * COS_ANGLE - pt.Y * SIN_ANGLE),                 (int)(pt.X * SIN_ANGLE + pt.Y * COS_ANGLE));        }    }}

RotatePt_1 cost time 00:00:02.2381280
RotatePt_2 cost time 00:00:01.7471000
RotatePt_3 cost time 00:00:01.5130866