[PD] removing NaN pure-pd

[Charles Henry]

> My best guess is that NaN's come from underflow, under normal
> circumstances.  I wish there would be an easy way to change this
> behavior via a compiler flag, but I don't think there is.
>
> It seems to be a more pervasive problem, and it's unreasonable to
> expect to add NaN handlers in application code.  Thank the IEEE
> standards for this gem.

I did some more searching around to find that someone has written just
such a handler for underflow here:
http://www.cenapad.unicamp.br/parque/manuais/Ibmcxx/complink/tasks/tutrapex.htm

The code uses the sigcontext struct when a floating point exception
occurs, to set the result to zero, once an underflow is created.

Underflow traps are enabled by (gcc) compiler flag -mfp-trap-mode=u

I'm really not sure about how all of this can be applied successfully.
 Has anyone implemented this kind of handler before?