Convert from DateTime to RFC822 date

Problem/Question/Abstract:

I was trying to convert a DateTime value to a RFC822 style date, so I asked to Paolo, a friend of mine, if he did know how it works. He found that on the Net. It's not perfect... someone as a better one?

Answer:

function DateTimeToRFC822(DTTime: TDateTime): string;
var
  IdX: Integer;
  SaveShortDayNames: array[1..7] of string;
  SaveShortMonthNames: array[1..12] of string;
const
  MyShortDayNames: array[1..7] of string = ('Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri',
    'Sat');
  MyShortMonthNames: array[1..12] of string = ('Jan', 'Feb', 'Mar', 'Apr', 'May',
    'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec');
begin
  if (ShortDayNames[1] = MyShortDayNames[1]) then
    Result := FormatDateTime('ddd, d mmm yyyy hh:mm:ss', DTTime)
  else
  begin
    for IdX := Low(ShortDayNames) to High(ShortDayNames) do
    begin
      SaveShortDayNames[IdX] := ShortDayNames[IdX];
      ShortDayNames[IdX] := MyShortDayNames[IdX];
    end;
    for IdX := Low(ShortMonthNames) to High(ShortMonthNames) do
    begin
      SaveShortMonthNames[IdX] := ShortMonthNames[IdX];
      ShortMonthNames[IdX] := MyShortMonthNames[IdX];
    end;
    Result := FormatDateTime('ddd, d mmm yyyy hh:mm:ss', DTTime);
    for IdX := Low(ShortDayNames) to High(ShortDayNames) do
      ShortDayNames[IdX] := SaveShortDayNames[IdX];
    for IdX := Low(ShortMonthNames) to High(ShortMonthNames) do
      ShortMonthNames[IdX] := SaveShortMonthNames[IdX];
  end;
end;