unnormal Intel 80-bit long doubles and isnanl

[Siddhesh Poyarekar]

On 11/26/20 12:57 AM, Joseph Myers wrote:
> I think it would be a pain to maintain test coverage for unnormals (and
> presumably all the other kinds of unsupported operands, and you'd need to
> work out what semantics you want for pseudo-denormals as well since those
> are the one kind of such representation the processor doesn't raise
> "invalid" for) for all the functions with floating-point arguments - and
> claiming to handle those consistently requires having such test coverage
> (there are only a few tests for such format-specific representations in
> sysdeps/ieee754/ldbl-96 at present).

pseudo-denormals are still considered valid, so I'm admittedly punting 
them for later since the processor manual still claims to handle them 
correctly.

> But maybe you could set up some mechanism by which, when gen-libm-test.py
> processes a test using snan_value or snan_value_ld (but not
> snan_value_pl), and the relevant format is one of the format variants that
> has these representations, it automatically generates tests for all those
> variants (that the processor raises "invalid" for when handling as
> operands, i.e. treats much like sNaN).  I'm not sure if it's actually
> possible to generate a static initializer for a long double value with one
> of those representations, or only for a union containing a long double
> where another member is initialized; if a union type needs to be used in
> the tables of test inputs, that further complicates things.
It would have to either be a union type with various bit patterns or a 
bit string copied into a long double; the CPU will never generate any of 
the pseudo numbers on its own.

Siddhesh