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Date: Sun, 24 May 2015 10:46:50 +0200 From: Nicholas Mc Guire <der.herr@...r.at> To: Joe Perches <joe@...ches.com> Cc: Steven Rostedt <rostedt@...dmis.org>, Nicholas Mc Guire <hofrat@...dl.org>, Lai Jiangshan <laijs@...fujitsu.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Josh Triplett <josh@...htriplett.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH RFC] rcu: change return type to bool On Sun, 24 May 2015, Joe Perches wrote: > On Sun, 2015-05-24 at 10:10 +0200, Nicholas Mc Guire wrote: > > On Sun, 24 May 2015, Joe Perches wrote: > > > > > 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. > > > > > As I understand this applies to arithmetic operations so for > > bool x = false; int i = 42; x += i; x is defined to be true > > but here it is the return type and not an arithmetic operation > > so does this apply here without the !!? > > Yes, it does. return is an implicit conversion. > > 6.8.6.4 The return statement > > 3 If a return statement with an expression is executed, the value of > the expression is returned to the caller as the value of the function > call expression. If the expression has a type different from the > return type of the function in which it appears, the value is > converted as if by assignment to an object having the return type of > the function. > get it - thanks for the clarification ! thx! hofrat -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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