NAME

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

SYNOPSIS

       #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():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
       isnan():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || _XOPEN_SOURCE
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
       isinf():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

       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.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).
       ┌──────────────────────────────┬───────────────┬─────────┐
       │ Interface                    │ Attribute     │ Value   │
       ├──────────────────────────────┼───────────────┼─────────┤
       │ fpclassify(), isfinite(),    │ Thread safety │ MT-Safe │
       │ isnormal(), isnan(), isinf() │               │         │
       └──────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, C99.

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

NOTES

       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.)

SEE ALSO

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

COLOPHON

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                                                   2017-09-15                                      FPCLASSIFY(3)