A question about fill_free_list(void) function

[Pedram]

On Jul 1, 10:01 pm, Christian Heimes <li... at cheimes.de> wrote:
> Pedram schrieb:
>
> > Hello community,
> > I'm reading the CPython interpreter source code,
> > first, if you have something that I should know for better reading
> > this source code, I would much appreciate that :)
> > second, in intobject.c file, I read the following code in
> > fill_free_list function that I couldn't understand:
> > <code>while (--q > p)
> >     Py_TYPE(q) = (struct _typeobject *)(q-1);
> > Py_TYPE(q) = NULL;
> > </code>
> > What does it mean?
>
> The code is abusing the ob_type member to store a single linked, NULL
> terminated list of free integer objects. It's a tricky optimization you
> don't have to understand in order to understand the rest of the code.
>
> And no, the code in ctypes.h is totally unrelated to the free list in
> intobject.c.
>
> Christian

Thanks for reply.
I totally understood the fill_free_list() function. Thanks.
But I have problems in understanding the PyInt_FromLong(). Here's the
code:

PyObject *
PyInt_FromLong(long ival)
{
	register PyIntObject *v;
#if NSMALLNEGINTS + NSMALLPOSINTS > 0
	if (-NSMALLNEGINTS <= ival && ival < NSMALLPOSINTS) {
		v = small_ints[ival + NSMALLNEGINTS];
		Py_INCREF(v);
#ifdef COUNT_ALLOCS
		if (ival >= 0)
			quick_int_allocs++;
		else
			quick_neg_int_allocs++;
#endif
		return (PyObject *) v;
	}
#endif
	if (free_list == NULL) {
		if ((free_list = fill_free_list()) == NULL)
			return NULL;
	}

	v = free_list; // <-- No problem till here :)
	free_list = (PyIntObject *)Py_TYPE(v);
	PyObject_INIT(v, &PyInt_Type);
	v->ob_ival = ival;
	return (PyObject *) v;
}

I understood that small numbers (between -5 and 256) are referenced to
small_ints list. Others have to store in PyIntBlock, am I right? OK,
no problem till 'v = free_list;' but can't understand the line
'free_list = (PyIntObject *)Py_TYPE(v);' :(. Where free_list
referenced to? Don't this correct that free_list have to be referenced
to another free block so next time the function called v store in this
location?
Sorry for my bad English. I hope you could understand me :)