IEEE-754 says that the result “should” be one of the two input NaNs. A platform could choose to e.g. take the NaN with the smaller payload to make * and + comm

IEEE-754 says that the result “should” be one of the two input NaNs. A platform could choose to e.g. take the NaN with the smaller payload to make * and + commutative, or it could simply define away NaN payloads entirely.