From: Guillaume Melquiond (guillaume.melquiond_at_[hidden])
Date: 2006-05-15 13:03:28
Le lundi 15 mai 2006 à 16:22 +0100, Paul A Bristow a écrit :
> Does this mean that the
>
> // C99 macros defined as C++ templates
> template<class T> bool signbit(T x);
>
> is undefined for a NaN?
No, it is perfectly defined as the value of the highest bit of the
binary representation. But whether or not it is actually carrying any
useful information is a whole other matter. NaN have sign bits but no
sign. :)
> I note that
>
> ISO/IEC 9899:1999 (E) 7.19.6.1p8:
>
> "A double argument representing an infinity is converted in one of the
> styles
> [-]inf or [-]infinity - which style is implementation-defined. A
> double argument representing a NaN is converted in one of the styles
> [-]nan or [-]nan(n-char-sequence)
>
> Explicitly allows a preceeding - sign.
>
> Seems like it is hard to justify prohibiting the - sign - but clearly its
> meaning is 'implementation defined'?
Right. My point was mainly about your sentence: "This allows for
positive and negative infinities, and for both positive and negative
quiet_NaN." I would simply avoid speaking of the sign for a NaN.
> Similarly interpretation of the suffix (n-char-sequence) is too - but how is
> the stream expected to know when it has ended?
I may be wrong, but it seems to me the parentheses are present in the
output, so the sequence trivially ends when the right parenthesis is
reached.
Best regards,
Guillaume