Usefulness of signaling NaN?

Question

I\'ve recently read up quite a bit on IEEE 754 and the x87 architecture. I was thinking of using NaN as a \"missing value\" in some numeric calculation code I\'m working on

Answer 1

Using special values (even NULL) can make your data a lot muddier and your code a lot messier. It would be impossible to distinguish between a QNaN result and a QNaN "special" value.

You might be better maintaining a parallel data structure to track validity, or perhaps having your FP data in a different (sparse) data structure to only keep valid data.

This is fairly general advice; special values are very useful in certain cases (e.g. really tight memory or performance constraints), but as the context grows larger they can cause more difficulty than they're worth.