byte[] startfile = File.ReadAllBytes("e:\\mylog.log");
byte[] comp = null;
byte[] decom = null;



 


comp = CompressBytes(startfile);
Console.WriteLine(comp.Length.ToString());


decom = Decompress(comp);
Console.WriteLine(decom.Length.ToString());
 

private void Compress(byte[] fileBytes)
{
    using(MemoryStream ms = new MemoryStream())
    {
        using(GZipStream gz = new GZipStream(ms, 
                                             CompressionMode.Compress, 
                                             true))
        {
            gz.Write(fileBytes, 0, fileBytes.Length);

            gz.Close();
        }
    }
}

private byte[] Decompress(byte[] fileBytes)
{
    int buffer_size = 100;

    using(MemoryStream ms = new MemoryStream(fileBytes))
    {
        using(GZipStream gz = new GZipStream(ms, 
                                             CompressionMode.Decompress, 
                                             true))
        {
            byte[] bufferFooter = null;
            int readOffset = 0;
            int totalBytes = 0;
            byte[] finalBuffer = null;
            int uncompLength = 0;
            int compressedFileLength = fileBytes.Length;

            // Get last 4 bytes (footer) as they contain the 
            // original length of the compressed bytes
            
            // byte array to hold footer value
            bufferFooter = new byte[4];

            // Set position of MemoryStream end of stream
            // minus the 4 bytes needed
            ms.Position = ms.Length - 4;
            
            // Fill the bufferFooter with the last 4 bytes
            ms.Read(bufferFooter, 0, 4);

            // Set Stream back to 0
            ms.Position = 0;

            // Convert footer bytes to the length.
            uncompLength = BitConverter.ToInt32(bufferFooter, 0);

            // Set a temporary buffer to hold the uncompressed
            // information. We also make it slightly larger to 
            // ensure everything will fit. We will later trim 
            // off the unused bytes.
            finalBuffer = new byte[uncompLength + buffer_size];

            while(true)
            {
                // Read from stream up to buffer size. Note that return
                // value is actual bytes read in case the number filled
                // is less than we requested.
                int bytesRead = gz.Read(finalBuffer, 
                                        readOffset, 
                                        buffer_size);

                // If no bytes returned we are done
                if(bytesRead == 0)
                {
                    break;
                }

                readOffset += bytesRead;
                totalBytes += bytesRead;
            }

            // Trim off unused bytes based 
            Array.Resize<byte>(ref finalBuffer, totalBytes);

            return finalBuffer;
        }
    }
}