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

On 8/6/26 09:42, Wilken Gottwalt wrote:
> 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

FWIW, one could argue that it is often misused in the Linux kernel.

> used in some places of the kernel. A lot of non-native English speakers report
> that as a typo. Ahh... just ignore my gibberish.
> 

Actually, any reasonable AI should be able to find that this isn't a problem
given the constraints. Sashiko didn't flag it, and if it did I'd have submitted
a prompt update. Sashiko is explicitly directed to check for over- and underflows
in hwmon patches because it happens so often, so I am (reasonably ;-) sure that it
would flag it if there was a problem.

If you are ok with the patch, any chance for a Tested-by/Acked-by/Reviewed-by ?

Thanks,
Guenter