Observations

The exact meaning of single, double, and extendedprecision is implementation defined.
Choosing the right precision for a problem where the choice matters requires significant understanding of floatingpoint computation.
If you don’t have that understanding, get advice, take the time to learn, or use double and hope for the best.

- Bjarne Stroustrup, The C++ Programming Language, Third Edition, 4.5 FloatingPoint Types.