Re: Conflicts between C standard and 754-2008
On Jan 6 2011, Hossam A. H. Fahmy wrote:
754 and 1788 members,
I followed the steps of Michel and tried to see if there are any other
issues with the C standard that conflict with 754-2008. I used the links
provided by Fred Tydeman on the current versions of the standard.
(http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf and
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1539.pdf)
It depends on what you mean.
If you mean conflicts where a clear requirement of C99 or C1X is flatly
incompatible with a clear requirement of IEEE 754, there are probably
very few. I know of none.
If you mean conflicts where a conforming C99 or C1X implementation
can set __STDC_IEC_559__ to 1 and still be incompatible with a clear
requirement of IEEE 754, there are dozens, perhaps hundreds. I have
mentioned a few on this mailing list in the past, but they are merely
a small subset of the clearer ones.
If you mean conflicts of a less definite nature, where the requirements
can reasonably be interpreted incompatibly or the intents are clearly
incompatible, it's impossible even to estimate.
I don't see any major difficulty in an implementation delivering formal
conformance with both standards, but it will be obviously be impossible
to write portable code that uses IEEE 754 as it was intended and relies
solely on the guaranteed properties. Whether a de facto interpretation
will emerge that makes it possible to write semi-portable code that does
is less clear.
Regards,
Nick Maclaren.