| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | Daniel Gustafsson <daniel(at)yesql(dot)se> |
| Cc: | Dagfinn Ilmari Mannsåker <ilmari(at)ilmari(dot)org>, Ewan Young <kdbase(dot)hack(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Andrey Rachitskiy <pl0h0yp1(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Subject: | Re: right() returns the whole string for the most negative n |
| Date: | 2026-08-26 12:55:39 |
| Message-ID: | CAApHDvrPHJKqUMpqRTUcbb=zBKyfJMWGG0-+nQCQ6Wch6kM+1g@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, 26 Aug 2026 at 00:33, Daniel Gustafsson <daniel(at)yesql(dot)se> wrote:
>
> > On 25 Aug 2026, at 14:18, Dagfinn Ilmari Mannsåker <ilmari(at)ilmari(dot)org> wrote:
> >
> > Instead of open-coding this, how about about using pg_neg_s32_overflow?
> >
> > if (pg_neg_s32_overflow(n, &n))
> > n = PG_INT32_MAX;
>
> Yes, that's indeed a good idea.
I do see a few places where we do check for PG_INT32_MIN instead of
using pg_neg_s32_overflow(). The example in [1] does end up with less
code as a result of using pg_neg_s32_overflow(), so it might be worth
removing all applicable examples that use the other method from master
as a follow-up. It'd be worth verifying it doesn't make anything worse
for build systems that don't have __builtin_sub_overflow().
David
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