The best I can think of is the IC code below

It allows me to get the same output as you, but I don't know that it proves the problem is in SvNV() because it also avoids sv_setnv().
And I've been assuming that the problem is inside sv_setnv().

I'll post a bug report (referencing this thread) later today and report the developments from that report back to this thread.

In the meantime, I'm happy to continue this discussion - though my thick skull may continue to defy the penetration of the points you make ;-)

With the code you just provided, running Devel::Peek::Dump($snan); crashes - which is a pity, because I would have liked to see more of what is in that variable.
And print $snan; outputs the same as pack 'd' done on a signalling NaN (that has the 7ff0000000000001 format).
The last line of code crashes for me (on a 32-bit perl that has quad formatting) - but that's no issue as the previous code had displayed: 
NaN
7ff0000000000001

[download]
and it was nice to see 7ff0000000000001 for a change.

The CCFLAGS setting in the I::C config has no impact afaict. (I assume it's a leftover from a previous exercise - and mention it only in case it should have provided something significant.)

Cheers,
Rob

In reply to Re^11: unintentional conversion of signaling NaN to quiet NaN by syphilis
in thread unintentional conversion of signaling NaN to quiet NaN by pryrt

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