Checking for a bit pattern

Question

I have an array of 30 bytes and need to parse through it checking for a 7 bit pattern of 0100111 when found move foward 233 bit into the next frame and check for the alternate pattern of 1011000 I'm having problems changing from a byte array to a bitarray can anyone point me in the right direction??

Mike Gold · Answer

A bit array will take an array of bytes in the constructor so you can just pass in the byte array. Alan's solution may be a little easier though. It doesn't seem that Microsoft provides a method to take a piece of the BitArray. CopyTo is the closest thing at this copies the entire array at a specific index. BitArray mainarray = new BitArray(myBytes); Theoretically their may be a way to do the comparison by sliding a BitArray with your pattern along the big bitarray record and the Xor method of the BitArray  also masking the other bits in the main array with 0000s (using the And method of the BitArray). Then use CopyTo to copy the entire contents to a boolean array and essentially search for a single true boolean value.

gordon · Answer

Thanks for responding I'll give it a try

Alan · Answer

If you don't mind using strings for this then the following approach should work. I've just used a 5 byte array for illustration and as expected the pattern is found at bit 17 (zero based): using System; using System.Text; class Program { static void Main() { byte[] ba = new byte[5]{1 2 39 4 5}; string pattern = 0100111; // decimal 39 StringBuilder sb = new StringBuilder(8 * ba.Length); int temp = 0; foreach (byte b in ba) { temp = int.Parse(Convert.ToString(b 2)); sb.Append(temp.ToString(00000000)); } string bitArray = sb.ToString(); Console.Clear(); Console.WriteLine(Bitarray is {0} bitArray); Console.WriteLine(Pattern is {0}
 pattern); int index = bitArray.IndexOf(pattern); if (index == -1) Console.WriteLine(Pattern wasn't found); else Console.WriteLine(Pattern first occurred at bit {0} index); Console.ReadKey(); } }