(j3.2006) Signaling NaN

[Tobias Burnus]

On 03/11/2011 06:19 PM, Bill Long wrote:
> The standard does specify some of this, and other parts are "processor 
> dependent".

Well, I think it specifies the general format: A NaN is printed. And as 
one can deduce from the input format, a signalling NaN, if printed as 
such, has the format "NaN(" + some non-zero-sized string + ")". (Though, 
the reverse does not work: If there are alphanumeric letters between the 
"()", it can still be a quiet NaN.)

> Note that the standard (inconsistently) requires that on INPUT, the 
> text is expected to be "NAN"

No, it does not: "A lower-case letter is equivalent to the corresponding 
upper-case letter in an IEEE exceptional specification or the exponent 
in a numeric input field."

> and on output it is "NaN".  We print NAN on output so is consistent 
> with input expectations.

While we (gfortran) print "NaN". (Ignoring the issue that gfortran still 
lacks an implementation of the TR 15580/Fortran 2008 IEEE modules.)

Tobias