Messages in this thread | | | Date | Wed, 5 Mar 2008 13:35:29 +0100 (MET) | From | Julia Lawall <> | Subject | Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & |
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On Wed, 5 Mar 2008, Ingo Molnar 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()".
!fn1() && !fn2() does not have the same semantics as !fn1() & !fn2(). In !fn1() & !fn2() both function calls are evaluated. In !fn1() && !fn2(), if !fn1() returns false then !fn2() is not evaluated. I haven't studied the particular instances of fn2(), though, to know whether it makes a difference.
One could instead do something like:
x = fn1(); y = fn2(); if (!x && !y) ...
It would certainly be clearer, but more verbose.
julia
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