First thought I had when reading about this is that the unused bits would be perfect for potentially reporting a cause of the NaN. A bit hackish, sure, but pote

First thought I had when reading about this is that the unused bits would be perfect for potentially reporting a cause of the NaN. A bit hackish, sure, but potentially useful, especially in C where you don't have exceptions that can carry human readable explanations of what wrong to arrive at a NaN.