New gnulib wrappers with glibc 2.21.

[Paul Eggert]

[Also cc'ing bug-gnulib.]
On 02/11/2015 08:05 AM, Joseph Myers wrote:
> These bit-patterns are considered to be trap representations

Yes, this is not a standards-conformance issue.

> with the gnulib implementation they are still trap representations 
> (not consistently behaving like NaNs), you've just made a different 
> choice of how to handle them.

Yes, as I understand it the original motivation for this was glibc bug 
4586 <https://sourceware.org/bugzilla/show_bug.cgi?id=4586>.  This bug 
caused GNU 'od' to crash when printing long double data, so we worked 
around the problem by using isnanl to determine whther a value was a 
printable number (as opposed to a trap representation that could cause 
core dumps).  Which meant that isnanl needed to return nonzero on 
non-canonical representations.

My impression is that this old problem is no longer relevant, and that 
we can remove the Gnulib requirement that isnanl must return nonzero on 
non-canonical representations.  This would mean Gnulib would no longer 
report problems with x86-64 glibc isnanl.

If I'm wrong and the old problem is still relevant, or if there's a need 
for this sort of check in the future, Gnulib should use the new 
iscanonical macro instead, as it's the one designed for the purpose that 
Gnulib was using isnanl for.