Re: infnan()?

[Ben Pfaff <pfaffben@pilot.msu.edu>]

   I would like to use NaN's.  It appears that isnan()
   works as advertised so I can check for NaN.  However,
   there is a man page for infnan() but no such function
   appears to be available.  Does anyone know the proper
   way to generate a NaN value?  (I am using NaN as an
   initialization value so that I can check that a valid
   value is used later.)  For the moment I am using NAN
   as defined in nan.h but it requires the use of
   "#define _GNU_SOURCE 1".  I would like to keep the code
   somewhat portable.

/* HUGE_VAL is traditionally defined as positive infinity, or
   alternatively, DBL_MAX. */
#if !HAVE_ISINF
#define isinf(X) 				\
	(fabs (X) == HUGE_VAL)
#endif

/* A Not a Number is not equal to itself. */
#if !HAVE_ISNAN
#define isnan(X) 				\
	((X) != (X))
#endif

/* Finite numbers are not infinities or NaNs. */
#if !HAVE_FINITE
#define finite(X) 				\
	(!isinf (X) && !isnan (X))
#elif HAVE_IEEEFP_H
#include <ieeefp.h>		/* Declares finite() under Solaris. */
#endif

The definition of infnan() is left as an exercise to the reader :-)


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