While f80 had some quirks it is an ieee754 floating point unit, and has all the ieee precision and semantics.

But my point was that saying floating point was somehow a magical non-deterministic beast is incorrect, and saying == shouldn't be allowed because of that is incorrect. Pretty much the same arguments can be made for integer arithmetic (after all x/y is undefined behavior if it overflows or y is zero even for integers, and just as with floating point you need to understand the behavior of arithmetic)