Date: Fri, 9 Jan 2009 16:00:09 GMT From: John Hein <jhein@timing.com> To: freebsd-standards@FreeBSD.org Subject: Re: standards/130067: Wrong numeric limits in system headers? Message-ID: <200901091600.n09G091i028176@freefall.freebsd.org>
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The following reply was made to PR standards/130067; it has been noted by GNATS.
From: John Hein <jhein@timing.com>
To: =?UTF-8?B?VsOhY2xhdiBIYWlzbWFu?= <v.haisman@sh.cvut.cz>
Cc: Bruce Evans <brde@optusnet.com.au>, das@FreeBSD.ORG, imp@FreeBSD.ORG,
freebsd-gnats-submit@FreeBSD.ORG, freebsd-standards@FreeBSD.ORG
Subject: Re: standards/130067: Wrong numeric limits in system headers?
Date: Fri, 9 Jan 2009 08:57:26 -0700
V=E1clav Haisman wrote at 22:56 +0100 on Jan 8, 2009:
> David Schultz wrote, On 6.1.2009 20:03:
> > On FreeBSD/i386, long doubles are represented with 64 bits of
> > precision, but computations are performed with 53 bits of
> > precision. In a sane world, this discrepancy wouldn't exist, but
> > for reasons I won't get into, they do, and probably always will.
> > =
> > C99 defines the LDBL constants based on what can be represented,
> > not what can be computed as the result of arithmetic operations,
> > so my interpretation is that the values in float.h are correct,
> > though confusing.
> I am not language lawyer but even if it were true that the constants a=
re
> right, there is still the problem that they (especially the LDBL_MAX v=
alue)
> are useless with the provided GCC. Either GCC or the headers should be=
> changed. Otherwise the constants are rather useless and unusable.
FWIW, when you compile the OP's sample code on i386 with -pedantic
(with 6.x's base gcc 3.4.6 or 7.x's base gcc 4.2.1), you get:
x.cc:11: error: floating constant exceeds range of 'long double'
(the LDBL_MAX line)
That seems to tip the scale more to the 'float.h is wrong' side.
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