[zokier]

Float determinism is one of those things that in theory floats should behave deterministically, but in practice it's a wild west. One big problem is that in C (and in many others), common operators are not explicitly mapped to specific fp operations, which gives compilers quite a lot of leeway on what they can do.

Another issue is that FP uses some amount of invisible global state, e.g. rounding modes. Iirc for example DirectX likes to change the flags behind your back.