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       fpclassify,   isfinite,   isnormal,   isnan,   isinf  -  floating-point
       classification macros


       #include <math.h>

       int fpclassify(x);

       int isfinite(x);

       int isnormal(x);

       int isnan(x);

       int isinf(x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       fpclassify(), isfinite(), isnormal(): _XOPEN_SOURCE >= 600 ||
       _ISOC99_SOURCE; or cc -std=c99
       isnan(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE ||
       _ISOC99_SOURCE; or cc -std=c99
       isinf(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
       _ISOC99_SOURCE; or cc -std=c99


       Floating  point  numbers  can  have special values, such as infinite or
       NaN.  With the macro fpclassify(x) you can find out  what  type  x  is.
       The  macro takes any floating-point expression as argument.  The result
       is one of the following values:

       FP_NAN        x is "Not a Number".

       FP_INFINITE   x is either positive infinity or negative infinity.

       FP_ZERO       x is zero.

       FP_SUBNORMAL  x is too small to be represented in normalized format.

       FP_NORMAL     if nothing of the above is correct  then  it  must  be  a
                     normal floating-point number.

       The other macros provide a short answer to some standard questions.

       isfinite(x)   returns a nonzero value if
                     (fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE)

       isnormal(x)   returns a nonzero value if (fpclassify(x) == FP_NORMAL)

       isnan(x)      returns a nonzero value if (fpclassify(x) == FP_NAN)

       isinf(x)      returns 1 if x is positive  infinity,  and  -1  if  x  is
                     negative infinity.


       C99, POSIX.1.

       For  isinf(), the standards merely say that the return value is nonzero
       if and only if the argument has an infinite value.


       In glibc 2.01 and earlier, isinf() returns a nonzero  value  (actually:
       1)  if  x is positive infinity or negative infinity.  (This is all that
       C99 requires.)


       finite(3), INFINITY(3), isgreater(3), signbit(3)


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                                  2008-08-07                     FPCLASSIFY(3)