>>6
As of C99, at least, the only point on which C floating point numbers are allowed to differ from IEEE 754 is when it comes to long doubles, where it says the following:
The long double type matches an IEC 60559 extended format, else a non-IEC 60559 extended format, else the IEC 60559 double format.
It later recommends that long doubles
should match an IEC 60559 extended format.
double and
float are guaranteed to be IEEE 754's double and single formats.
(IEC 60559 is an alias for IEEE 754.)