function TBufferedFileStream.Seek(const Offset: Int64; Origin: TSeekOrigin): Int64;
var
  lNewOffset: int64;
begin
  Case Origin of
    soEnd:
      begin
        lNewOffset:=FCacheStreamSize+Offset;
      end;
    soBeginning:
      begin
        lNewOffset:=0+Offset;
      end;
    soCurrent:
      begin
        lNewOffset:=FCacheStreamPosition+Offset;
      end;
  end;
  if lNewOffset>0 then begin
    FCacheStreamPosition:=lNewOffset;
    Result:=lNewOffset;
  end else begin
    // This is compatible with FPC stream
    // as it returns the negative value :-?
    // but in fact does not move the read pointer.
    Result:=-1;
  end;
end;