"F.2 Types

The C floating types match the IEC 60559 formats as follows:

— The float type matches the IEC 60559 single format.

— The double type matches the IEC 60559 double format.

— The long double type matches an IEC 60559 extended format, else a non-IEC 60559 extended format, else the IEC 60559 double format.

Any non-IEC 60559 extended format used for the long double type shall have more precision than IEC 60559 double and at least the range of IEC 60559 double.

Recommended practice

The long double type should match an IEC 60559 extended format."

ISO/IEC 9899:1999, Annex F