function NewExMemoryStream( ExistingMem: Pointer; Size: DWORD ): PStream;
begin
  Result := NewMemoryStream;
  Result.fMemory := ExistingMem;
  Result.fData.fCapacity := Size;
  Result.fData.fSize := Size;
  Result.fMethods.fWrite := WriteExMemoryStream;
  Result.fMethods.fSetSiz := DummySetSize;
  Result.fMethods.fClose := DummyClose_ExMemStream;
end;