Function tbm_intersect

src/backend/nodes/tidbitmap.c:563–608

* tbm_intersect - set intersection * * a is modified in-place, b is not changed */

 * a is modified in-place, b is not changed
 */
void
tbm_intersect(TIDBitmap *a, const TIDBitmap *b)
{
	Assert(!a->iterating);
	/* Nothing to do if a is empty */
	if (a->nentries == 0)
		return;

	a->nentries_hwm = Max(a->nentries_hwm, a->nentries);

	/* Scan through chunks and pages in a, try to match to b */
	if (a->status == TBM_ONE_PAGE)
	{
		if (tbm_intersect_page(a, &a->entry1, b))
		{
			/* Page is now empty, remove it from a */
			Assert(!a->entry1.ischunk);
			a->npages--;
			a->nentries--;
			Assert(a->nentries == 0);
			a->status = TBM_EMPTY;
		}
	}
	else
	{
		pagetable_iterator i;
		PagetableEntry *apage;

		Assert(a->status == TBM_HASH);
		pagetable_start_iterate(a->pagetable, &i);
		while ((apage = pagetable_iterate(a->pagetable, &i)) != NULL)
		{
			if (tbm_intersect_page(a, apage, b))
			{
				/* Page or chunk is now empty, remove it from a */
				if (apage->ischunk)
					a->nchunks--;
				else
					a->npages--;
				a->nentries--;
				if (!pagetable_delete(a->pagetable, apage->blockno))
					elog(ERROR, "hash table corrupted");
			}
		}
	}
}

/*
 * Process one page of a during an intersection op