fpclassify(3)

1FPCLASSIFY(3)              Linux Programmer's Manual             FPCLASSIFY(3)
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NAME

6       fpclassify, isfinite, isnormal, isnan, isinf - floating-point classifi‐
7       cation macros
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SYNOPSIS

10       #include <math.h>
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12       int fpclassify(x);
13       int isfinite(x);
14       int isnormal(x);
15       int isnan(x);
16       int isinf(x);
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18       Link with -lm.
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20   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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22       fpclassify(), isfinite(), isnormal():
23           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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25       isnan():
26           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
27               || _XOPEN_SOURCE
28               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
29               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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31       isinf():
32           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
33               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
34               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

37       Floating point numbers can have special values,  such  as  infinite  or
38       NaN.   With  the  macro  fpclassify(x) you can find out what type x is.
39       The macro takes any floating-point expression as argument.  The  result
40       is one of the following values:
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42       FP_NAN        x is "Not a Number".
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44       FP_INFINITE   x is either positive infinity or negative infinity.
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46       FP_ZERO       x is zero.
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48       FP_SUBNORMAL  x is too small to be represented in normalized format.
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50       FP_NORMAL     if nothing of the above is correct then it must be a nor‐
51                     mal floating-point number.
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53       The other macros provide a short answer to some standard questions.
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55       isfinite(x)   returns a nonzero value if
56                     (fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE)
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58       isnormal(x)   returns a nonzero value if (fpclassify(x) == FP_NORMAL)
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60       isnan(x)      returns a nonzero value if (fpclassify(x) == FP_NAN)
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62       isinf(x)      returns 1 if x is positive infinity, and -1 if x is nega‐
63                     tive infinity.
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ATTRIBUTES

66       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
67       tributes(7).
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69       ┌────────────────────────────────────────────┬───────────────┬─────────┐
70       │Interface                                   │ Attribute     │ Value   │
71       ├────────────────────────────────────────────┼───────────────┼─────────┤
72       │fpclassify(), isfinite(), isnormal(),       │ Thread safety │ MT-Safe │
73       │isnan(), isinf()                            │               │         │
74       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

77       POSIX.1-2001, POSIX.1-2008, C99.
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79       For  isinf(), the standards merely say that the return value is nonzero
80       if and only if the argument has an infinite value.
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NOTES

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

91       This page is part of release 5.13 of the Linux  man-pages  project.   A
92       description  of  the project, information about reporting bugs, and the
93       latest    version    of    this    page,    can     be     found     at
94       https://www.kernel.org/doc/man-pages/.
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98                                  2021-03-22                     FPCLASSIFY(3)