Re: tgamma and CX

[David-Sarah Hopwood <david.hopwood@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

Geoff Clare wrote:
>   If the correct value would cause underflow, [CX]and is not
>   representable[/CX], a range error may occur, and [CX MX] either 0.0
>   (if supported), or [/CX MX] an implementation-defined value shall be
>   returned.
I don't understand the intent of "either 0.0 (if supported), or
an implementation-defined value". Is it that:

a) an implementation can document some value other than 0.0, but
   return 0.0 anyway?
b) it just means "an implementation-defined value", but that 0.0
   is the preferred value?
c) 0.0 shall be returned if __STDC_IEC_559__ is defined; otherwise
   the return value is implementation-defined.

If a), why is that desirable?
If b), why not put the statement that 0.0 is preferred in a footnote?
If c), using "or" here is a very unclear way of stating the intent.

--
David-Sarah Hopwood