Re: [Tinycc-devel] NAN and INFINITY break in different ways

[Michael Matz]

Hi,

On Sun, 24 Dec 2017, Vincent Lefevre wrote:

> > I think we could make an exception for 0.0/0.0 and always fold this into NaN
> > (normally division by zero is indeed not allowable in constant expressions
> > in c99).
>
> AFAIK, the standard just implies that 0.0/0.0 is not specified as a
> constant expression. But the standard also says: "An implementation
> may accept other forms of constant expressions."
>
> Moreover, if Annex F is supported, then FP division by zero is
> well-defined. F7.4.2 gives examples with 0.0/0.0 in initializers,
> such as:
>
>  static float x = 0.0/0.0; // does not raise an exception
>
> Nowadays, supporting Annex F is more or less a must.

Right you are.  There are differences in rules for accepting integer 
constant expressions and "mere" constant expressions used e.g. for static 
initializers.  They can (and with annex F have to) be accepted and FP 
exceptions be ignored at translation time.  (Not so for non-static 
initializers where the exceptions need to be raised at runtime).

Fixed in mob.


Ciao,
Michael.