TDSC = Packed Record
  dsc_dtype     :Byte;
  dsc_scale     :Byte;
  dsc_length    :Word;
  dsc_sub_type  :Word;
  dsc_flags     :Word;
  dsc_address   :Pointer;
End;
PDSC = ^TDSC;

Function __ExtractDouble(AData :PAnsiChar): PDSC; CDecl; Export;
Var d :double;
Begin
  Result := Nil; // тут NULL возврошает

  d := 123.456;
  Result := d; // вот как тут мои double в result запыхнуть ???

End;

DECLARE EXTERNAL FUNCTION XD_EXTRACTSTRINGPART
    CSTRING(256),
    CSTRING(256) BY DESCRIPTOR
RETURNS PARAMETER 2
ENTRY_POINT '__ExtractStringPart' MODULE_NAME 'xdUDF';

Function __ExtractStringPart(AString :PAnsiChar; AParam :PDSC): PDSC; CDecl; Export;
Var S :String;
Begin
  S := 'qaqa';
  AParam.dsc_address := @S;
  Result := AParam;
End;