Re: right() returns the whole string for the most negative n - Mailing list pgsql-hackers

> On 27 Aug 2026, at 07:17, Ewan Young <kdbase.hack@gmail.com> wrote:
> On Thu, Aug 27, 2026 at 10:45 AM David Rowley <dgrowleyml@gmail.com> wrote:

>> Also, pg_neg_s32_overflow() was introduced in 2024 by 0a27c3d0f733,
>> which is v18+. Depending on Daniel's patience for backpatching two
>> different versions, it might be worth just using the == PG_INT32_MIN
>> method to fix the bug, then allowing the follow-up patch to switch
>> that in v20 only.  That would mean v18 and v19 don't get the most
>> optimal fix, but it's hard to imagine that's going to be performance
>> critical.
>
> Thanks, that plan makes sense to me -- let's keep the bug fix uniform
> across all branches and do the pg_neg_s32_overflow() switch separately.

FWIW, I agree with this plan.

> Attached v4 goes back to the explicit PG_INT32_MIN test:
>
>    if (unlikely(n == PG_INT32_MIN))
>        n = PG_INT32_MAX;
>    else
>        n = -n;
>
> which applies cleanly to every supported branch (I checked REL_14 through
> REL_19 and master).  The fix and the regression case are otherwise
> unchanged.

I will prepare a backpatch all the way of this, and will ping the new thread
when done.  (There is a lof work being done for shipping v19 so have a little
patience.)

> I'll take the pg_neg_s32_overflow() cleanup to its own thread, master
> only, covering the other open-coded negation checks Ilmari pointed at
> (int2/4/8 um/abs/div, lcm, cash, numericvar_to_int64); once this fix
> lands I'll fold text_right() into that too.  So the back-branches keep the
> plain form and only master gets the helper.

+1

--
Daniel Gustafsson