[Cfp-interest 2327] Re: infinity and exceptions

[Vincent Lefevre]

On 2022-01-13 21:06:35 -0800, Fred J. Tydeman wrote:
> On Fri, 14 Jan 2022 14:22:00 +1100 (AEDT) Damian McGuckin wrote:
> >
> >On Thu, 13 Jan 2022, Fred J. Tydeman wrote:
> >>How about adding to 5.2.4.2.2 #16 and #17:
> >>16: The evaluation of INFINITY does not raise any FP exceptions.
> >>17: The evaluation of NAN does not raise any FP exceptions.

OK for me.

> >Yes. But then again, how do you evaluate NAN?

Just like any expression.

> >You can assign it.

Other things can be done, not just assignments. Even

  (void) NAN;

is an evaluation.

> I have been sent the output of a program that did
>   float f;
>   f = NAN;
> and the raised overflow, inexact, and invalid.
> My guess:  It appears that NAN was defined as (INFINITY * 0.f)
> and INFINITY was defined as (LDBL_MAX * LDBL_MAX)

Indeed, that's incorrect, concerning the exceptions, but also
the values when rounding toward zero could be used (one would
get LDBL_MAX for INFINITY and 0 for NAN), and the types too.

-- 
Vincent Lefèvre <vincent at vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)