Re: Remove dependence on integer wrapping

On Tue, Jun 11, 2024 at 09:31:39AM -0400, Joseph Koshakow wrote:
> tmp is an uint16 here, it seems like you might have read it as an
> int16? We would need some helper method like
>
> static inline bool
> pg_neg_u16_overflow(uint16 a, int16 *result);
>
> and then we could replace that whole chunk with something like
>
> if (unlikely(pg_neg_u16_overflow(tmp, &result)))
> goto out_of_range;
> else
> return result;
>
>
> that pattern shows up a lot in this file, but I was worried that it
> wasn't useful as a general purpose function. Happy to add it
> though if you still feel otherwise.

I personally find that much easier to read. Since the existing open-coded
overflow check is apparently insufficient, I think there's a reasonably
strong case for centralizing this sort of thing so that we don't continue
to make the same mistakes.

>> Ah, I see. Joe's patch does that in one place. It's probably worth doing
>> that in the other places this "just-barefly overflow" comment appears
>> IMHO.
>
> The only other place I found this comment was in
> `make_timestamp_internal`. I've updated that function and added some
> tests. I also manually verified that the behavior matches before and
> after this patch.

tm2timestamp() in src/interfaces/ecpg/pgtypeslib/timestamp.c has the same
comment. The code there looks very similar to the code for tm2timestamp()
in the other timestamp.c...

--
nathan