To make a game like an RTS networked, I've seen a number of answers here suggest to make the game completely deterministic; then you only have to transfer the users' actions to each other, and lag what's displayed a little bit in order to "lock in" everyone's input before the next frame is rendered. Then things like unit's positions, health, etc. don't need to be constantly updated over the network, because every player's simulation will be exactly the same. I've also heard the same thing suggested for making replays.
However, since floating-point calculations are non-deterministic between machines, or even between different compilations of the same program on the same machine, is this really possible to do? How do we prevent that fact from causing small differences between players (or replays) that ripple throughout the game?
I've heard some people suggest avoiding floating-point numbers altogether and using
int to represent the quotient of a fraction, but that doesn't sound practical to me - what if I need to, for example, take the cosine of an angle? Do I seriously need to rewrite an entire math library?
Note that I am mainly interested in C#, which as far as I can tell, has exactly the same problems as C++ in this regard.