I would like -if possible at all- to represent and handle missing data (in the statistical sense) within the standard IEEE-754 format. Seeing that for both SNaNs and QNaNs various bit representations are possible, I wonder if they all can arise from standard computations or some can be made inaccessible to paths other than the corresponding explicit bit storage, and thus safe and reserved to represent "empty slots" for missing data.
So first of all, does the standard dictate a specific behaviour in representing NaNs or can each processor/system treat them differently? And in the former case, can I do what's hinted at above? (assuming it's safe to detect such values e.g. in C++ via static_cast or a union)
The IEEE standard generically dictates NaN for certain undefined operations, however not the specific payloads. I wonder if there is a standard de facto for this. I would not care if external libraries each have their own payloads, but it's a more serious matter if standard C++ libs are not consistent.