FPCLASSIFY
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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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(),
isnormal(),
isnan(),
isinf()
| Thread safety | MT-Safe
|
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
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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- Running on 
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