- BSD floating-point classification functions

       #include <math.h>

       int finite(double x);
       int finitef(float x);
       int finitel(long double x);

       int isinf(double x);
       int isinff(float x);
       int isinfl(long double x);

       int isnan(double x);
       int isnanf(float x);
       int isnanl(long double x);

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

       finite(), finitef(), finitel():
           _BSD_SOURCE || _SVID_SOURCE
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
           or cc -std=c99
       isinff(), isinfl():
           _BSD_SOURCE || _SVID_SOURCE
           or cc -std=c99
       isnanf(), isnanl():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600

       The finite(), finitef(), and finitel() functions return a nonzero value
       if x is neither infinite nor a "not-a-number" (NaN) value, and 0 other-

       The isnan(), isnanf(), and isnanl() functions return a nonzero value if
       x is a NaN value, and 0 otherwise.

       The isinf(), isinff(), and isinfl() functions return 1 if x is positive
       infinity, -1 if x is negative infinity, and 0 otherwise.

   Multithreading (see pthreads(7))
       The   finite(),  finitef(),  finitel(),  isinf(),  isinff(),  isinfl(),
       isnan(), isnanf(), and isnanl() functions are thread-safe.

       Note that these functions are obsolete.  C99 defines macros isfinite(),
       isinf(), and isnan() (for all types) replacing them.  Further note that
       the C99 isinf() has weaker guarantees on the return value.  See fpclas-
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