Date: Thu, 11 Jul 2013 11:37:20 +0200 From: Tijl Coosemans <tijl@FreeBSD.org> To: Bruce Evans <brde@optusnet.com.au> Cc: Garrett Wollman <wollman@csail.mit.edu>, FreeBSD CURRENT <freebsd-current@FreeBSD.org>, freebsd-standards@FreeBSD.org, freebsd-toolchain@FreeBSD.org Subject: Re: CURRENT: CLANG 3.3 and -stad=c++11 and -stdlib=libc++: isnan()/isninf() oddity Message-ID: <51DE7CD0.60306@FreeBSD.org> In-Reply-To: <20130711130043.R920@besplex.bde.org> References: <20130710155809.0f589c22@thor.walstatt.dyndns.org> <CD51F125-AE9E-4461-916D-CF583002B47D@FreeBSD.org> <20130710183315.725dfde0@thor.walstatt.dyndns.org> <C8C94CF2-7D5A-471B-AD63-8E961AED6274@FreeBSD.org> <20130710203200.5359fd18@thor.walstatt.dyndns.org> <51DDC04B.6040209@FreeBSD.org> <20957.49978.73666.392417@khavrinen.csail.mit.edu> <20130711130043.R920@besplex.bde.org>
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On 2013-07-11 06:21, Bruce Evans wrote:
> On Wed, 10 Jul 2013, Garrett Wollman wrote:
>> <<On Wed, 10 Jul 2013 22:12:59 +0200, Tijl Coosemans <tijl@freebsd.org=
> said:
>>> I think isnan(double) and isinf(double) in math.h should only be
>>> visible if (_BSD_VISIBLE || _XSI_VISIBLE) && __ISO_C_VISIBLE < 1999.
>>> For C99 and higher there should only be the isnan/isinf macros.
>>
>> I believe you are correct. POSIX.1-2008 (which is aligned with C99)
>> consistently calls isnan() a "macro", and gives a pseudo-prototype of
>>
>> int isnan(real-floating x);
>=20
> Almost any macro may be implemented as a function, if no conforming
> program can tell the difference. It is impossible for technical reason=
s
> to implement isnan() as a macro (except on weird implementations where
> all real-floating types are physically the same). In the FreeBSD
> implementation, isnan() is a macro, but it is also a function, and
> the macro expands to the function in double precision:
>=20
> % #define isnan(x) \
> % ((sizeof (x) =3D=3D sizeof (float)) ? __isnanf(x) \
> % : (sizeof (x) =3D=3D sizeof (double)) ? isnan(x) \
> % : __isnanl(x))
The C99 standard says isnan is a macro. I would say that only means
defined(isnan) is true. Whether that macro then expands to function
calls or not is not important.
> I don't see how any conforming program can access the isnan() function
> directly. It is just as protected as __isnan() would be. (isnan)()
> gives the function (the function prototype uses this), but conforming
> programs can't do that since the function might not exist.
I don't think the standard allows a function to be declared with the same=
name as a standard macro (it does allow the reverse: define a macro with
the same name as a standard function). I believe the following code is
C99 conforming but it currently does not compile with our math.h:
------
#include <math.h>
=20
int (isnan)(int a, int b, int c) {
return (a + b + c);
}
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