Am 17.02.22 um 18:44 schrieb John Maddock via Boost:
Does anyone have a (non-theoretical) use case for signalling quad-precision NaN's? And or a working test case?
Thanks, John.
Crap, neither does snanf128, of course; hope that's it then :-) https://godbolt.org/z/v854oG8E5
That generates a NaN that has the same general appearance as a double-precision signalling NaN, but I'm unable to actually make it *signal*. Unless this is supported by GCC and libquadmath, it still looks to me that there are no signalling NaN's for __float128? To repeat myself: do you have a working test case where signalling NaN's actually do something useful? Otherwise it looks to me as though has_signalling_NaN really should be false?
John.
The difference between the values is (exponent: all bits set, sign bit cleared (libquadmath), https://en.wikipedia.org/wiki/NaN) qnan: the most significant fraction bit must be set and/or any fraction bit must be set snan: the most significant fraction bit must be clear and any fraction bit set. libquadmath always sets the second highest fraction bit. I don't have a real example either, but std::isnan should work. thx Gero