Re: Add bms_offset_members() function for bitshifting Bitmapsets

On Sat, Aug 22, 2026, at 9:38 PM, David Rowley wrote:
> On Thu, 9 Jul 2026 at 11:55, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
>> I pushed a change to make seed int64 instead. It's still possible to
>> specify the full range of possible values that GetCurrentTimestamp()
>> can (or could ever) return with the int64 type. This way, there's no
>> longer a mismatch in the format specifier for elog and the type we're
>> formatting. That's an improvement, so thanks.

Hey David,

> I was just in this area again and noticed that the nmembers
> calculation does not take into account the min_value parameter. The
> bad code is:
>
> nmembers = pg_prng_uint32(&state) % max_range + min_value;

Indeed, good catch.

> That should really be subtracting the min_value, as I had intended
> nmembers to do was populate a random set of members in the range
> specified by the function. While there, I noticed that the parameter
> names are not very consistently named and having the max_value before
> the min_value seems weird too.

I agree that is an implicit convention and is more intuitive.

> I understand test_random_operations()
> has it that way. I didn't adjust that function. Maybe that could be
> done separately since it's also in v19, whereas
> test_random_offset_operations() is new to v20.

I think this is a good idea, simply to be consistent/tidy and re-enforce the pattern for future work.

> I've attached a patch which fixes this plus a few more things that
> Claude code pointed out to me when I asked it to review my changes.
> Those are primarily around overflow risk if max_value was given as
> INT32_MAX.

I applied, reviewed, and tested the v1 patch. I think it is good and necessary for the reasons you've outlined. I'd happily help or implement the additional test_random_operations() for v20/v19 when I get a second (currently traveling) if you're not going to do so.

Thanks for continuing to improve this testing module.

best.

-greg

> David
>
> Attachments:
> * v1-0001-Fix-incorrect-nmembers-calculation-in-test_bitmap.patch