System.IO.FileStream.SeekCore C# (CSharp) Method

        private long SeekCore(long offset, SeekOrigin origin)
        {
            Debug.Assert(!_fileHandle.IsClosed && _canSeek, "!_handle.IsClosed && _parent.CanSeek");
            Debug.Assert(origin >= SeekOrigin.Begin && origin <= SeekOrigin.End, "origin>=SeekOrigin.Begin && origin<=SeekOrigin.End");
            long ret = 0;

            if (!Interop.Kernel32.SetFilePointerEx(_fileHandle, offset, out ret, (uint)origin))
            {
                int errorCode = GetLastWin32ErrorAndDisposeHandleIfInvalid();
                throw Win32Marshal.GetExceptionForWin32Error(errorCode);
            }

            _filePosition = ret;
            return ret;
        }