[Octave-bug-tracker] [bug #40668] -NA is inconsistent with other operations on NA

[Daniel Kraft]

Follow-up Comment #5, bug #40668 (project octave):

As I understand it, doesn't IEEE 754 allow for distinct (quiet) NaN values, of
which NA is a particular one?  Those values should be propagated through all
computations, so as long as you don't perform operations between NA and NaN
but only between NA and ordinary numbers, NA should be preserved (also for
external codes that "just" do calculations with the numbers passed in).

The sign bit is a bit different from the NaN payload bits, and thus seemingly
the unary minus flips the sign bit even though the payload itself stays the
same as it should.  Based on this interpretation, it makes sense to me to
ignore the sign bit when checking for NA.  However, I understand that it is
probably best not to rely on this behaviour in one's code (and I have changed
mine already accordingly).

Are there possible problems that can be introduced by modifying
__lo_ieee_is_NA() accordingly?

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