They're deterministic but partially implementation defined. Some instructions don't guarantee the maximum possible precision, and implementations can differ in

They're deterministic but partially implementation defined. Some instructions don't guarantee the maximum possible precision, and implementations can differ in the least significant bits of their result. Addition and multiplication give you the correctly rounded result. However, there is typically some leeway in fma fusion. That is, if you multiply then add, it is in some cases implementation defined whether you get a result that was rounded after the multiplication and before the addition, or you get the correctly rounded result of doing the multiply and add as one operation without intermediate rounding. All this is with the most conservative compiler settings. Be very, very careful about your optimization settings. And let's not get into nans. All this adds up to a situation where writing floating point code that is guaranteed to produce the same bit exact result on all implementations is basically a superhuman task. Better to just use fixed point and be done with it.