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copied!<p>The Boyer-Moore algorithm that is used in grep is pretty efficient, and gets more efficient for longer pattern sizes. I'm pretty sure you could make it work for a byte array without too much difficulty, and its <a href="http://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_string_search_algorithm" rel="noreferrer">wikipedia page</a> has an implementation in Java that should be fairly easy to port to C#.</p> <p>UPDATE:</p> <p>Here's an implementation of a simplified version of the Boyer-Moore algorithm for byte arrays in C#. It only uses the <a href="http://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_string_search_algorithm#The_second_table" rel="noreferrer">second jump table</a> of the full algorithm. Based on the array sizes that you said (haystack: 2000000 bytes, needle: 10 bytes), it's about 5-8 times faster than a simple byte by byte algorithm.</p> <pre><code> static int SimpleBoyerMooreSearch(byte[] haystack, byte[] needle) { int[] lookup = new int[256]; for (int i = 0; i < lookup.Length; i++) { lookup[i] = needle.Length; } for (int i = 0; i < needle.Length; i++) { lookup[needle[i]] = needle.Length - i - 1; } int index = needle.Length - 1; var lastByte = needle.Last(); while (index < haystack.Length) { var checkByte = haystack[index]; if (haystack[index] == lastByte) { bool found = true; for (int j = needle.Length - 2; j >= 0; j--) { if (haystack[index - needle.Length + j + 1] != needle[j]) { found = false; break; } } if (found) return index - needle.Length + 1; else index++; } else { index += lookup[checkByte]; } } return -1; } </code></pre>

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