SIMPLE SOLUTIONS

# ILOGB(3) - man page online | library functions

Get integer exponent of a floating-point value.

Chapter
2015-04-19
```ILOGB(3)                            Linux Programmer's Manual                            ILOGB(3)

NAME
ilogb, ilogbf, ilogbl - get integer exponent of a floating-point value

SYNOPSIS
#include <math.h>

int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);

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

ilogb():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
ilogbf(), ilogbl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99

DESCRIPTION
These functions return the exponent part of their argument as a signed integer.  When no
error occurs, these functions are equivalent to the corresponding logb(3) functions, cast
to int.

RETURN VALUE
On success, these functions return the exponent of x, as a signed integer.

If x is zero, then a domain error occurs, and the functions return FP_ILOGB0.

If x is a NaN, then a domain error occurs, and the functions return FP_ILOGBNAN.

If x is negative infinity or positive infinity, then a domain error occurs, and the func‐
tions return INT_MAX.

ERRORS
See math_error(7) for information on how to determine whether an error has occurred when
calling these functions.

The following errors can occur:

Domain error: x is 0 or a NaN
An invalid floating-point exception (FE_INVALID) is raised, and errno is set to
EDOM (but see BUGS).

Domain error: x is an infinity
An invalid floating-point exception (FE_INVALID) is raised, and errno is set to
EDOM (but see BUGS).

ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).

┌────────────────────────────┬───────────────┬─────────┐
│Interface                   │ Attribute     │ Value   │
├────────────────────────────┼───────────────┼─────────┤
│ilogb(), ilogbf(), ilogbl() │ Thread safety │ MT-Safe │
└────────────────────────────┴───────────────┴─────────┘
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.

BUGS
Before version 2.16, the following bugs existed in the glibc implementation of these func‐
tions:

*  The domain error case where x is 0 or a NaN did not cause errno to be set or (on some
architectures) raise a floating-point exception.

*  The domain error case where x is an infinity did not cause errno to be set or raise a
floating-point exception.