function IsDaylightSaving: Boolean;
var
  Dummy: Windows.TTimeZoneInformation; // info about time zone
begin
  Result := False;
  case Windows.GetTimeZoneInformation(Dummy) of
    Windows.TIME_ZONE_ID_INVALID: SysUtils.RaiseLastOSError;
    Windows.TIME_ZONE_ID_DAYLIGHT: Result := True;
  end;
end;
//delphi/2173