是什么使Enum.HasFlag这么慢？

Z时代
2024-01-10
分类：问答

我在进行一些速度测试时，发现Enum.HasFlag比使用按位运算慢大约16倍。

有谁知道Enum.HasFlag的内部原理，为什么它这么慢？我的意思是说慢两倍不会太糟糕，但是当它慢16倍时，它会使该功能不可用。

如果有人想知道，这里是我用来测试其速度的代码。

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
namespace app
{
    public class Program
    {
        [Flags]
        public enum Test
        {
            Flag1 = 1,
            Flag2 = 2,
            Flag3 = 4,
            Flag4 = 8
        }
        static int num = 0;
        static Random rand;
        static void Main(string[] args)
        {
            int seed = (int)DateTime.UtcNow.Ticks;
            var st1 = new SpeedTest(delegate
            {
                Test t = Test.Flag1;
                t |= (Test)rand.Next(1, 9);
                if (t.HasFlag(Test.Flag4))
                    num++;
            });
            var st2 = new SpeedTest(delegate
            {
                Test t = Test.Flag1;
                t |= (Test)rand.Next(1, 9);
                if (HasFlag(t , Test.Flag4))
                    num++;
            });
            rand = new Random(seed);
            st1.Test();
            rand = new Random(seed);
            st2.Test();
            Console.WriteLine("Random to prevent optimizing out things {0}", num);
            Console.WriteLine("HasFlag: {0}ms {1}ms {2}ms", st1.Min, st1.Average, st1.Max);
            Console.WriteLine("Bitwise: {0}ms {1}ms {2}ms", st2.Min, st2.Average, st2.Max);
            Console.ReadLine();
        }
        static bool HasFlag(Test flags, Test flag)
        {
            return (flags & flag) != 0;
        }
    }
    [DebuggerDisplay("Average = {Average}")]
    class SpeedTest
    {
        public int Iterations { get; set; }
        public int Times { get; set; }
        public List<Stopwatch> Watches { get; set; }
        public Action Function { get; set; }
        public long Min { get { return Watches.Min(s => s.ElapsedMilliseconds); } }
        public long Max { get { return Watches.Max(s => s.ElapsedMilliseconds); } }
        public double Average { get { return Watches.Average(s => s.ElapsedMilliseconds); } }
        public SpeedTest(Action func)
        {
            Times = 10;
            Iterations = 100000;
            Function = func;
            Watches = new List<Stopwatch>();
        }
        public void Test()
        {
            Watches.Clear();
            for (int i = 0; i < Times; i++)
            {
                var sw = Stopwatch.StartNew();
                for (int o = 0; o < Iterations; o++)
                {
                    Function();
                }
                sw.Stop();
                Watches.Add(sw);
            }
        }
    }
}