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INFINITY, NAN, HUGE_VAL, HUGE_VALF, HUGE_VALL - floating-point
#define _ISOC99_SOURCE /* See feature_test_macros(7) */
The macro INFINITY expands to a float constant representing positive
The macro NAN expands to a float constant representing a quiet NaN
(when supported). A quiet NaN is a NaN ("not-a-number") that does not
raise exceptions when it is used in arithmetic. The opposite is a
signaling NaN. See IEC 60559:1989.
The macros HUGE_VAL, HUGE_VALF, HUGE_VALL expand to constants of types
double, float and long double, respectively, that represent a large
positive value, possibly plus infinity.
On a glibc system, the macro HUGE_VAL is always available.
Availability of the NAN macro can be tested using #ifdef NAN, and
similarly for INFINITY, HUGE_VALF, HUGE_VALL. They will be defined by
<math.h> if _ISOC99_SOURCE or _GNU_SOURCE is defined, or
__STDC_VERSION__ is defined and has a value not less than 199901L.
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