FPCLASSIFY(3) Linux Programmer's Manual FPCLASSIFY(3)NAME
fpclassify, isfinite, isnormal, isnan, isinf - floating-point classifi‐
cation 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(): _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
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 nor‐
mal floating-point number.
The other macros provide a short answer to some standard questions.
isfinite(x) returns a non-zero value if
(fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE)
isnormal(x) returns a non-zero value if (fpclassify(x) == FP_NORMAL)
isnan(x) returns a non-zero value if (fpclassify(x) == FP_NAN)
isinf(x) returns 1 if x is positive infinity, and -1 if x is nega‐
tive infinity.
CONFORMING TO
C99, POSIX.1.
For isinf(), the standards merely say that the return value is non-zero
if and only if the argument has an infinite value.
NOTES
In glibc 2.01 and earlier, isinf() returns a non-zero value (actually:
1) if x is positive infinity or negative infinity. (This is all that
C99 requires.)
SEE ALSOfinite(3), INFINITY(3), isgreater(3), signbit(3)COLOPHON
This page is part of release 3.15 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2008-08-07 FPCLASSIFY(3)