Indeed. In clause 4 of Section 6.5.13 of C99, short circuit evaluation
is guaranteed in addition to left to right evaluation.
On 11/2/10, Stefan Richter <stefanr@xxxxxxxxxxxxxxxxx> wrote:
> Lukas Czerner wrote:
>> On Tue, 2 Nov 2010, kevin granade wrote:
>>> + if (time_after_eq(jiffies, elr->lr_next_sched) &&
>>> + ext4_run_li_request(elr) != 0) {
>>> + /* error, remove the lazy_init job */
>>> + ext4_remove_li_request(elr);
>>> + continue;
>>> }
>>>
>>> if (time_before(elr->lr_next_sched, next_wakeup))
>>> --
>>>
>>> Though obviously it's a pretty subjective style issue.
>>> Kevin Granade
>>
>> Hmm this relies on the fact that if the first part of the condition
>> would not be true, the second part (after and) would never be invoked,
>> however I am not really sure that we can rely on that on every
>> architecture, or can we ?
>
> It is not about architecture but a C language feature. It is relied upon
> everywhere in the kernel. For example,
>
> if (p != NULL && p->m == something) {
> ...
>
> is very common. The || operator has the same property: Evaluation stops as
> soon as the end result is known. I do not know since when this minimum
> evaluation feature is guaranteed in the language, but it has to be ages now.
>
> (This is not an endorsement of one or the other coding of the patch. :-)
> --
> Stefan Richter
> -=====-==-=- =-== ---=-
> http://arcgraph.de/sr/
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>
--
Brian Gitonga Marete
Toshnix Systems
Tel: +254722151590
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
