Re: [PATCH v2] hwmon: (corsair-psu) Fix linear11 calculation

On Thu, 6 Aug 2026 09:28:34 -0700
Guenter Roeck <[email protected]> wrote:

> On 8/6/26 08:56, Wilken Gottwalt wrote:
> ...
> >>>> +	s64 result = mant * scale;
> >>>
> >>> Uhm, this is a 32bit multiplicaiton, actully a C gotcha I explain the beginners
> >>> in our company. https://godbolt.org/z/eM6TbGG5E
> >>>
> >>
> >> It is, but that is ok and intentional: both mant and exp are guaranteed to be
> >> no larger than s16, meaning the result is never larger than s32 and will never
> >> overflow.
> >>
> >>>> -	return (exp >= 0) ? (result << exp) : (result >> -exp);
> >>>> +	if (exp >= 0)
> >>>> +		result *= (int)(1UL << exp);
> >>
> >> This is the calculation that can overflow, making it necessary for result to be s64.
> > 
> > Yeah, it was just funny to see in the wild. It made my day. :D
> > 
> 
> Guess I lost you there. Do you want me to change it ? I could add a comment, or just
> type cast mant to s64. Please let me know.

No no, it is fine. I just was surprised to see that famous gotcha. But I guess
some AIs may jump on it, ignoring the context. Changing it maybe would prevent
noise in the future. It is like that famous mathematical "iff" term, which is
used in some places of the kernel. A lot of non-native English speakers report
that as a typo. Ahh... just ignore my gibberish.

greetings,
Wilken