本文告诉大家几个方法从 byte 数组找到对应的相同序列的数组

最简单的方法是进行数值判断,但是代码最少是使用Linq ,效率比较高是使用 Boyer-Moore 算法,下面就告诉大家几个算法的代码

判断数值

    class ByteArrayRocks
    {
        public static IEnumerable<int> IndexOf(byte[] source, int start, byte[] pattern)
        {
            if (IsEmptyLocate(source, start, pattern))
            {
                yield break;
            }

            for (int i = start; i < source.Length; i++)
            {
                if (!IsMatch(source, i, pattern))
                {
                    continue;
                }

                yield return i;
            }
        }

        private static readonly int[] Empty = new int[0];

        private static bool IsMatch(byte[] array, int position, byte[] candidate)
        {
            if (candidate.Length > (array.Length - position))
            {
                return false;
            }

            for (int i = 0; i < candidate.Length; i++)
            {
                if (array[position + i] != candidate[i])
                {
                    return false;
                }
            }

            return true;
        }

        private static bool IsEmptyLocate(byte[] array, int start, byte[] candidate)
        {
            return array == null
                   || candidate == null
                   || array.Length == 0
                   || array.Length < start
                   || candidate.Length == 0
                   || candidate.Length + start > array.Length;
        }
    }

这是最简单的方法,参见 https://stackoverflow.com/a/283648/6116637

linq

这个方法的代码最少

    class LinqArraySearch
    {
        public static IEnumerable<int> IndexOf(byte[] source, int start, byte[] pattern)
        {
            for (int i = start; i < source.Length; i++)
            {
                if (source.Skip(i).Take(pattern.Length).SequenceEqual(pattern))
                {
                    yield return i;
                }
            }
        }
    }

Boyer-Moore-Horspool 搜索

这是最快的方法

    class BoyerMooreHorspool
    {
        public static IEnumerable<long> IndexesOf(byte[] source, int start, byte[] pattern)
        {
            if (source == null)
            {
                throw new ArgumentNullException(nameof(source));
            }

            if (pattern == null)
            {
                throw new ArgumentNullException(nameof(pattern));
            }

            long valueLength = source.LongLength;
            long patternLength = pattern.LongLength;

            if ((valueLength == 0) || (patternLength == 0) || (patternLength > valueLength))
            {
                yield break;
            }

            var badCharacters = new long[256];

            for (var i = 0; i < 256; i++)
            {
                badCharacters[i] = patternLength;
            }

            var lastPatternByte = patternLength - 1;

            for (long i = 0; i < lastPatternByte; i++)
            {
                badCharacters[pattern[i]] = lastPatternByte - i;
            }

            long index = start;

            while (index <= valueLength - patternLength)
            {
                for (var i = lastPatternByte; source[index + i] == pattern[i]; i--)
                {
                    if (i == 0)
                    {
                        yield return index;
                        break;
                    }
                }

                index += badCharacters[source[index + lastPatternByte]];
            }
        }
    }

参见:https://stackoverflow.com/q/16252518/6116637

测试了三个方法的性能,请看下面


BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17134
Intel Core i7-6700 CPU 3.40GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=2.1.202
  [Host]     : .NET Core 2.0.9 (CoreCLR 4.6.26614.01, CoreFX 4.6.26614.01), 64bit RyuJIT
  DefaultJob : .NET Core 2.0.9 (CoreCLR 4.6.26614.01, CoreFX 4.6.26614.01), 64bit RyuJIT


Method Mean Error StdDev
Linq 13,332.8 us 251.782 us 466.694 us
ByteArrayRocks 371.3 us 7.327 us 14.462 us
BoyerMooreHorspool 108.3 us 1.153 us 1.079 us

其他方法请看下面

使用不安全代码的 Boyer Moore 算法 C# High Performance Boyer Moore Byte Array Search Algorithm


本文会经常更新,请阅读原文: https://dotnet-campus.github.io//post/C-%E5%AF%B9-byte-%E6%95%B0%E7%BB%84%E8%BF%9B%E8%A1%8C%E6%A8%A1%E5%BC%8F%E6%90%9C%E7%B4%A2.html ,以避免陈旧错误知识的误导,同时有更好的阅读体验。

知识共享许可协议 本作品采用 知识共享署名-非商业性使用-相同方式共享 4.0 国际许可协议 进行许可。欢迎转载、使用、重新发布,但务必保留文章署名 lindexi (包含链接: https://dotnet-campus.github.io/ ),不得用于商业目的,基于本文修改后的作品务必以相同的许可发布。如有任何疑问,请 与我联系