ArtemisComm.Utility.CopyTo C# (CSharp) Метод

        public static void CopyTo(this Stream sourceStream, Stream targetStream, int sourceIndex, long length)
        {
            if (targetStream != null)
            {
                long longlength = length;
                byte[] buffer = GetBuffer(sourceStream, sourceIndex);
                if (buffer.Length < longlength)
                {
                    longlength = buffer.Length;
                }

                int ln = 0;


                //Okay, I'm nuts to do this--but I guess I like to plan for all contingencies.
                do
                {
                    if (longlength < int.MaxValue)
                    {
                        ln = Convert.ToInt32(longlength);
                        longlength = 0;
                    }
                    else
                    {
                        ln = int.MaxValue;
                        longlength -= int.MaxValue;
                    }
                    targetStream.Write(buffer, 0, ln);
                } while (longlength > 0);
            }

        }
        public static MemoryStream GetMemoryStream(this Stream stream, int index)