Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and &

Bart Van Assche
2008-03-05T12:31:16Z

On Wed, Mar 5, 2008 at 1:20 PM, Ingo Molnar <mingo@elte.hu> wrote:
>
> * Julia Lawall <julia@diku.dk> wrote:
>
> > There are some legitimate uses of !x & y which are actually of the
> > form !x & !y, where x and y are function calls. That is a not
> > particularly elegant way of getting both x and y to be evaluated and
> > then combining the results using "and". If such code is considered
> > acceptable, then perhaps the sparse patch should be more complicated.
>
> i tend to be of the opinion that the details in C source code should be
> visually obvious and should be heavily simplified down from what is
> 'possible' language-wise - with most deviations and complications that
> depart from convention considered an error. I'd consider "!fn1() &
> !fn2()" a borderline coding style violation in any case - and it costs
> nothing to change it to "!fn1() && !fn2()".

If someone writes (!x & !y) instead of (!x && !y) because both x and y
have to be evaluated, this means that both x and y have side effects.
Please keep in mind that the C language does not specify whether x or
y has to be evaluated first, so if x and y have to be evaluated in
that order, an expression like (!x & !y) can be the cause of very
subtle bugs. I prefer readability above brevity.

Bart Van Assche.