benchmarking Poly/ML & floating point

[Stephen Weeks]

> The IEEE spec says that comparisons (equal, not-equal, less, ...) all return
> false if either is a NAN, but I don't know what the ML spec says.  There are
> strong arguments for NOT requiring this in a language spec.  It would mean
> that you can't efficiently reverse branch conditions, for instance.

The SML spec requires IEEE compliance.  It also says that != is equivalent to
"not o ==", which is the same as the IEEE ?<> operator.

I now believe I understand what is going on.  In C, x != y is exactly equivalent
to !(x == y).  Thus, the definitions of Real_nequal and Real_equal in
mlton-lib.h are correct.  Although there's still no reason I can see for keep
around the primitive Real_nequal, since it is just not o Real.==.  As to
Real.qequal, I bet the definition in mlton-lib.h is wrong, since it is
equivalent (I believe) to Real_equal.  I don't know if there is a way to get
what we want in one C operator.  So, my bet as to the right thing to do is to
drop Real_qequal as a primitive and to define Real.qequal in the basis library
as

val op ?= = fn (x, y) => isNan x orelse isNan y orelse x == y