Actually, the rounding for basic add/multiply are strictly defined and configurable (some algorithms need other rounding rules than the default "round to neares

Actually, the rounding for basic add/multiply are strictly defined and configurable (some algorithms need other rounding rules than the default "round to nearest even"). If you only use those (maybe including division, I'm not sure), and don't rely on hardware support for sqrt, sin/cos/tan, approximate-inverse, etc., you can totally use them deterministically between different architectures.