Fourth Draft "Unsafe fp optimizations" project description.

[Jason Riedy]

And Brad Lucier writes:
 - It is true that -0.0 is numerically equal to 0.0, but it not (Lisp)
 - equivalent, in that 1.0/(0.0) is most definitely not (numerically equal ||
 - equivalent || or identical) to 1.0/(-0.0).

Yes.  However, the _only_ two ways to determine the sign of
zero (short of bitops) are copysign and division.  The sign
is meant to be ignored 99.9999% of the time.  These 
transformations _may_ be reasonable in a default mode if
they allow good optimizations.

The original 754 proposal also included a projective mode
where there was only one infinity.  In that case, the only
way to see the sign was copysign.  Alas, it went away,
horribly complicating complex arithmetic.

Jason