NaNs and infinities
The floating point system supports two special representations:
Infinity
Positive infinity in a format compares greater
than all other representable numbers in the same format.
Arithmetic operations on infinities are quite intuitive.
For example, adding any representable number to infinity is
a valid operation the result of which is positive
infinity. Subtracting positive infinity from itself is
invalid. If some arithmetic operation overflows, and the
overflow trap is disabled, in some rounding modes the
result is infinity.
NotaNumber (NaN)
These floating point representations are not numbers. They
can be used to carry diagnostic information. There are two
kinds of NaNs: signaling NaNs and quiet NaNs. Signaling
NaNs raise the invalid operation exception whenever they
are used as operands in floating point operations. Quiet
NaNs propagate through most operations without raising any
exception. The result of these operations is the same
quiet NaN. NaNs are sometimes produced by the arithmetic
operations themselves. For example, 0.0 divided by 0.0,
when the invalid operation trap is disabled, produces a
quiet NaN.
The header file ieeefp.h defines the interface for
the floating point exception and environment control. This
header defines three interfaces:

Rounding control

Exception control

Exception handling
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Rounding control
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Specialcase values
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