Re: [PATCH RFC] rcu: change return type to bool

Joe Perches
2015-05-24T07:42:05Z

On Sun, 2015-05-24 at 09:27 +0200, Nicholas Mc Guire wrote:
> On Sat, 23 May 2015, Steven Rostedt wrote:
[]
> > > - return sum;
> > > + return !!sum;
> >
> > Hmm I wonder if gcc is smart enough to do the above without the need
> > for !!? That is, will it turn to !! because the return of the function
> > is bool, or does gcc complain about it not being bool without the !!?
> > Not a criticism of the patch, just a curiosity.
> >
> gcc will not complain if you assign a unsigned long to a boolean
> as I understand it it is a macro and is not doing any type
> checking/promotion at all - so anything can be assigned to a bool
> without warning (including double and pointers).
> The !! will though always make the type compatible with int so it is
> a well defined type atleast as far as __builtin_types_compatible_p()
> goes, and !! also makes static code checkers happy (that are maybe not
> as smart as gcc) and it does make the intent of sum being treated
> as boolean here clear.

6.3.1.2 Boolean type

When any scalar value is converted to _Bool, the result is 0 if the
value compares equal to 0; otherwise, the result is 1.