function Endian64(X: Int64): Int64;
begin
  Result :=          (X and $00000000000000FF) shl 56;
  Result := Result + (X and $000000000000FF00) shl 40;
  Result := Result + (X and $0000000000FF0000) shl 24;
  Result := Result + (X and $00000000FF000000) shl 8;
  Result := Result + (X and $000000FF00000000) shr 8;
  Result := Result + (X and $0000FF0000000000) shr 24;
  Result := Result + (X and $00FF000000000000) shr 40;
  Result := Result + (X and $FF00000000000000) shr 56;
end;

function Endian64(X: Int64): Int64;
type
  Ti64 = packed record
    Lo, Hi: LongWord;
  end;
begin
  Ti64(Result).Lo := Endian(Ti64(X).Hi);
  Ti64(Result).Hi := Endian(Ti64(X).Lo);
end;