On Thu, Jan 6, 2022 at 7:00 AM Trent Nelson <tr...@trent.me> wrote:
>
> I did some research on this a few years back.  I was curious what sort
> of "max reference counts" were encountered in the wild, in long-running
> real life programs.  For the same reason: I wanted to get some insight
> into how many unused bits could possibly be repurposed for future
> shenanigans (I had PyParallel* in the mind at the time).
>

I think we can assume the upper bound of the reference count is same
to upper bound of the pointer.
On 32bit machine, memory space is 2**32 byte, and pointers take
4bytes. And NULL can not store pointer. So upper bound of refcnt is
2**30-1.
So we have two free bits in the refcnt.

On 64bit machine, we have at least four free bits as same reason.

Regards,

-- 
Inada Naoki  <songofaca...@gmail.com>
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