Re: How to check a Float for NaN

["Stuart" <stuart@0.0>]

"Adam Beneschan" <adam@irvine.com> wrote in message 
news:93b0d930-102a-4ac4-8b85-48e87d9d3df1@j33g2000pri.googlegroups.com...
> On Apr 30, 3:50 am, christoph.gr...@eurocopter.com wrote:
>> On 30 Apr., 12:47, christoph.gr...@eurocopter.com wrote:
>>
>> > Try Float'Valid (X), see RM 13.9.2
>>
>> Ahem, I meant X'Valid for X of type Float
<snip>

> The problem here is that if you're dealing with NaN's on purpose,
> you're not really dealing with Ada, as far as I can tell, unless your
> purpose is to test for an uninitialized variable (in which case
> X'Valid makes sense).  Otherwise, though, NaN's and infinities are not
> possible values of floating-point types, and therefore they can't be
> returned by operations that return floating-point values, even if
> Float'Machine_Overflows is False.  (There are certain passages in the
> RM that say a result is implementation-defined if the
> Machine_Overflows attribute is False; however, I do not think
> assigning a variable to an invalid value, as a NaN would be, is an
> allowed "implementation-defined" result.  13.9.2(4-11) lists the ways
> that invalid data could be created, and the "result of a floating-
> point operation that cannot return a valid result" is not one of those
> listed.  Yes, I know that this is a NOTE and is not normative.)

Would not 13.9.2(10) cover this:
   "disrupting an assignment due to the failure of a language-defined check 
(see 11.6)"

Thus if a floating point operation creates a NaN, which would indicate an 
ill-conditioned computation that should violate some language-defined check, 
the object (X) that was to receive the result would be considered invalid.

As noted elsewhere, 'valid encompasses more than NaNs - which may or may not 
suit the OPs purpose.

Regards
-- 
Stuart