standards/130067: Wrong numeric limits in system headers?
John Hein
jhein at timing.com
Fri Jan 9 17:07:47 UTC 2009
Václav 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 are
> right, there is still the problem that they (especially the LDBL_MAX value)
> 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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