Their attempts to "preserve IEEE FP "negative zero"", performs + -0.0, which will *always* force SNaN to QNaN

Yes - that does seem pretty general behaviour, but I'm not concerned about that.
In fact, I've come to the view that if an operation involving an SNAN does not throw an exception then the result might just as well be a QNAN - since the SNAN is effectively quiet anyway.
Perhaps that's the rationale behind the behaviour.

I see no reason to expect that an operation involving an SNAN cannot not return a QNAN when no exception is thrown and I can even see a case for propagating the SNAN as a QNAN.
However, I don't know what the relevant IEEE standards stipulate - and, obviously if this behaviour contravenes said standards then the behaviour should be changed.

The following won't work pre-5.10, and may not work on some later builds

On 32-bit 5.22.0, 5.24.0 and latest blead the NV still gets set to 7ff8000000000001. (I didn't try any other perl versions.)

I don't personally need to be able to assign a double with internal representation of 7ff0000000000001, though I do think it's at least worth raising awareness of this bug in the 32-bit Windows builds.
But first I'll make a concerted effort to find a way to make that assignment.

Cheers,
Rob

In reply to Re^7: 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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