Re: Making empty Bitmapsets always be NULL

On Thu, 15 Jun 2023 at 20:57, Yuya Watari <watari.yuya@gmail.com> wrote:
>
> On Tue, Jun 13, 2023 at 8:07 PM David Rowley <dgrowleyml@gmail.com> wrote:
> > For the fix in the 0004 patch, I think we can do what you did more
> > simply.  I don't think there's any need to perform the loop to find
> > the last non-zero word.  We're only deleting a member from a single
> > word here, so we only need to check if that word is the last word and
> > remove it if it's become zero.  If it's not the last word then we
> > can't remove it as there must be some other non-zero word after it.
>
> If my thinking is correct, the do-while loop I added is still
> necessary. Consider the following code. The Assertion in this code
> passes in the master but fails in the new patch.
>
> =====
> Bitmapset *x = bms_make_singleton(1000);
>
> x = bms_del_member(x, 1000);
> Assert(x == NULL);
> =====

I'm not sure what I was thinking there.  Yeah, you're right, we do
need to do the backwards loop over the set to trim off the trailing
zero words.

I've adjusted the attached patch to do that.

David