尽量使用ToUpper比较，避免使用ToLower

在编码时尽量使用ToUpper比较，避免使用ToLower，因为微软对ToUpper进行了优化，以下为测试结果:

        public void TestToLower()
 
        {
 
            Stopwatch watch = new Stopwatch();
 
            Int32 count = 1000 * 1000;
 
            // ToUpper测试开始
 
            String lowerStr = "abcdefghijklmnopqrstuvwxyz";
 
            watch = Stopwatch.StartNew();
 
            for (int i = 0; i < count; i++)
 
            {
 
                lowerStr.ToUpper();
 
            }
 
            Console.WriteLine("ToUpper:{0}", watch.Elapsed.ToString());
 
            //ToLower测试开始
 
            String upperStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
 
            watch = Stopwatch.StartNew();
 
            for (int i = 0; i < count; i++)
 
            {
 
                upperStr.ToLower();
 
            }
 
            Console.WriteLine("ToLower:{0}", watch.Elapsed.ToString());
 
        }

结果为：

ToUpper:00:00:00.2598023 ToLower:00:00:00.2697799