True, but why would you need a floor? It's a rather arbitrary function.
This is a fundamental problem shared by any form of exact real arithmetic with unique representations; you can always then be forced to make a choice, before emitting any information, that depends on infinite amounts of information about the operands. To solve this problem, you would need to choose a representation with redundancy. (With redundancy, equality comparison becomes harder, and it can still diverge, but you can still get approximations of the answer.)