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  1. using System;
  2. using System.Diagnostics;
  3.  
  4. namespace ConsoleApplication1 {
  5.  
  6.   internal class Program {
  7.  
  8.     /// <summary>Looks for the next occurrence of a sequence in a byte array</summary>
  9.     /// <param name="array">Array that will be scanned</param>
  10.     /// <param name="start">Index in the array at which scanning will begin</param>
  11.     /// <param name="sequence">Sequence the array will be scanned for</param>
  12.     /// <returns>
  13.     ///   The index of the next occurrence of the sequence of -1 if not found
  14.     /// </returns>
  15.     private static int findSequence(byte[] array, int start, byte[] sequence) {
  16.       int end = array.Length - sequence.Length; // past here no match is possible
  17.       byte firstByte = sequence[0]; // cached to tell compiler there's no aliasing
  18.  
  19.       while(start <= end) {
  20.         // scan for first byte only. compiler-friendly.
  21.         if(array[start] == firstByte) {
  22.           // scan for rest of sequence
  23.           for (int offset = 1;; ++offset) {
  24.             if(offset == sequence.Length) { // full sequence matched?
  25.               return start;
  26.             } else if(array[start + offset] != sequence[offset]) {
  27.               break;
  28.             }
  29.           }
  30.         }
  31.         ++start;
  32.       }
  33.  
  34.       // end of array reached without match
  35.       return -1;
  36.     }
  37.  
  38.     private static void checkSingleByteSequence() {
  39.       byte[] sequence = new byte[] { 123 };
  40.  
  41.       Debug.Assert(findSequence(new byte[] { 123 }, 0, sequence) == 0);
  42.       Debug.Assert(findSequence(new byte[] { 100 }, 0, sequence) == -1);
  43.  
  44.       Debug.Assert(findSequence(new byte[] { 123, 124, 125 }, 0, sequence) == 0);
  45.       Debug.Assert(findSequence(new byte[] { 122, 123, 124 }, 0, sequence) == 1);
  46.       Debug.Assert(findSequence(new byte[] { 121, 122, 123 }, 0, sequence) == 2);
  47.  
  48.       Debug.Assert(findSequence(new byte[] { 123, 124, 125, 126 }, 1, sequence) == -1);
  49.       Debug.Assert(findSequence(new byte[] { 122, 123, 124, 125 }, 2, sequence) == -1);
  50.       Debug.Assert(findSequence(new byte[] { 123, 124, 123, 124 }, 1, sequence) == 2);
  51.       Debug.Assert(findSequence(new byte[] { 120, 121, 122, 123 }, 3, sequence) == 3);
  52.       Debug.Assert(findSequence(new byte[] { 121, 122, 123, 124 }, 3, sequence) == -1);
  53.     }
  54.  
  55.     private static void checkThreeByteSequence() {
  56.       byte[] sequence = new byte[] { 150, 150, 160 };
  57.  
  58.       Debug.Assert(findSequence(new byte[] { 100 }, 0, sequence) == -1);
  59.       Debug.Assert(findSequence(new byte[] { 100, 200 }, 0, sequence) == -1);
  60.       Debug.Assert(findSequence(new byte[] { 100, 110 }, 1, sequence) == -1);
  61.       Debug.Assert(findSequence(new byte[] { 100, 110, 120 }, 0, sequence) == -1);
  62.       Debug.Assert(findSequence(new byte[] { 100, 110, 120, 130 }, 3, sequence) == -1);
  63.  
  64.       Debug.Assert(findSequence(new byte[] { 150 }, 0, sequence) == -1);
  65.       Debug.Assert(findSequence(new byte[] { 100, 150 }, 0, sequence) == -1);
  66.       Debug.Assert(findSequence(new byte[] { 150, 150 }, 1, sequence) == -1);
  67.       Debug.Assert(findSequence(new byte[] { 100, 150, 150, 150 }, 0, sequence) == -1);
  68.       Debug.Assert(findSequence(new byte[] { 150, 150, 120, 150 }, 3, sequence) == -1);
  69.  
  70.       Debug.Assert(findSequence(new byte[] { 150, 150, 160, 170 }, 0, sequence) == 0);
  71.       Debug.Assert(findSequence(new byte[] { 150, 150, 160, 170 }, 1, sequence) == -1);
  72.  
  73.       Debug.Assert(findSequence(new byte[] { 140, 150, 150, 160 }, 0, sequence) == 1);
  74.       Debug.Assert(findSequence(new byte[] { 140, 150, 150, 160 }, 1, sequence) == 1);
  75.       Debug.Assert(findSequence(new byte[] { 140, 150, 150, 160 }, 2, sequence) == -1);
  76.     }
  77.  
  78.     public static void Main(string[] args) {
  79.       checkSingleByteSequence();
  80.       checkThreeByteSequence();
  81.     }
  82.  
  83.   }
  84.  
  85. }
Success #stdin #stdout 0.01s 13968KB
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https://ideone.com/mmACYj
language:
C# (gmcs 5.20.1)
created:
5 years ago
visibility:
public

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