At this point, with your Smaug-related comment, etc-- I've become convinced you're trolling.

But just to humor you: the desire is to have a system where floating point neither surprisingly kills nor gives characters extra hit points. There's a lot of subtlety in this. Schemes where all damage are percents don't preserve the essential pieces of RPG combat systems. Moving the threshold from 1 to 0 HP violates the conventions of the art and doesn't eliminate the problems (you can still end up with hit points epsilon away from 0, instead of 1).

The problem isn’t hitpoints that are an epsilon away from 1, it’s that an operation which looked innocuous moved the HP to an epsilon _below_ 1. That would never happen with 0, however, as multiplication and division of positive numbers always gives a positive result.

And in D&D, incapacitation happens when a character drops below 0 HP, and death happens once they drop below -10HP. There is no grand convention that all RPG games follow here; each game is making things up as they go. They picked badly when they designed Age of Empires, and that’s ok. It’s not the end of the world. Just know that we can do better if we are paying attention.

And I am serious when I ask “so what?”. Why is it so bad if the game displays 0/55HP? The players all know that fractional HP damage exists, and they can see that their unit is still alive, so what is the problem? They will be at least as amazed that their unit survived as they currently are when they see a unit at 1/55HP.

I am likewise serious about Smaug; there is no way that combat makes any sense if Smaug has a large number of hitpoints or that any weapon at all can damage him. Using hitpoints as an abstraction completely loses all of the flavor of Tolkien’s original descriptions. A better model is one using damage reduction and sensible internal organs; a strike that pierces the heart will kill even a dragon.

> however, as multiplication and division of positive numbers always gives a positive result.

Depends on what you do with subnormals and underflow, etc.

> There is no grand convention that all RPG games follow here

Computer RPGs have shown 0/812 for dead for ... forever.

> The players all know that fractional HP damage exists

I think most players will be confused. And for what, to make it "safe" doing floating point operations in the wrong order? (I doubt it's still safe, overall).

> I am likewise serious about Smaug; there is no way that combat makes any sense if Smaug has a large number of hitpoints or that any weapon at all can damage him.

Common mechanisms: an armor class that makes it hard to hit; a fixed amount of damage reduction so that a needle does nothing; a lot of hitpoints.

> and sensible internal organs;

It gets excessively complicated and annoying. Battletech is already excessively complicated, and doesn't go quite as far as you're advocating for here.