Get start position of byte chunk from a byte array

Question

Supposing I have a byte array of size 4096, what's an efficient way to get the start position of a chunk of say... 5 bytes that matches a pattern?

For e.g., I would like to get the start position of the 1st possible match of the byte array

var match = new byte[] { 0x03, 0x04, 0x05, 0x06, 0x07 };

So if the above chunk is found within my byte array, it will return me the position of the 1st byte (0x03)

if your search pattern in {0x03, 0x05}, what would you expect to see like a result? — Tigran, Jul 01 '13 at 08:43
This might help you: http://stackoverflow.com/questions/3028768/net-regular-expressions-on-bytes-instead-of-chars — Regenschein, Jul 01 '13 at 08:43
Also see this answer which uses the Boyer-Moore pattern matching algorithm (which is probably what I'd go for): http://stackoverflow.com/a/9890164/106159 — Matthew Watson, Jul 01 '13 at 08:48
+1 for the `Boyer-Moore's` pattern, it's quite efficient as it skips bytes that would not match rather than brute-forcing through all the bytes. — keyboardP, Jul 01 '13 at 08:50

Ahmed KRAIEM · Accepted Answer · 2013-07-01T09:01:50.353

You can use Linq:

public static int IndexOfArray<T>(T[] source, T[] search)
{

    var result = Enumerable.Range(0, source.Length - search.Length)
                           .Select(i => new
                           {
                               Index = i,
                               Found = source.Skip(i)
                                  .Take(search.Length)
                                  .SequenceEqual(search)
                           })
                           .FirstOrDefault(e => e.Found);
    return result == null ? -1 : result.Index;
}

Get start position of byte chunk from a byte array

1 Answers1