FPCLASSIFY

Section: Linux Programmer's Manual (3)
Updated: 2008-08-07
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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(): _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 normal 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 negative 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.)

COLOPHON

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