Get GUID from interface reference

function GetInterfaceEntry(const I: IInterface): PInterfaceEntry;
var
  Instance: TObject;
  InterfaceTable: PInterfaceTable;
  j: integer;
  CurrentClass: TClass;
begin
  Instance := I as TObject;
  if Assigned(Instance) then
  begin
    CurrentClass := Instance.ClassType;
    while Assigned(CurrentClass) do
    begin
      InterfaceTable := CurrentClass.GetInterfaceTable;
      if Assigned(InterfaceTable) then
        for j := 0 to InterfaceTable.EntryCount-1 do
        begin
          Result := @InterfaceTable.Entries[j];
          if Result.IOffset <> 0 then
          begin
            if Pointer(NativeInt(Instance) + Result^.IOffset) = Pointer(I) then
              Exit;
          end;
          // TODO: implement checking interface implemented via implements delegation
          // see System.TObject.GetInterface/System.InvokeImplGetter
        end;
      CurrentClass := CurrentClass.ClassParent
    end;
  end;
  Result := nil;
end;

function GetInterfaceIID(const I: IInterface; var IID: TGUID): boolean;
var
  InterfaceEntry: PInterfaceEntry;
begin
  InterfaceEntry := GetInterfaceEntry(I);
  Result := Assigned(InterfaceEntry);
  if Result then
    IID := InterfaceEntry.IID;
end;