NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

BUGS

SEE ALSO

COLOPHON

## NAME

## SYNOPSIS

## DESCRIPTION

## RETURN VALUE

## ERRORS

## ATTRIBUTES

## CONFORMING TO

## BUGS

## SEE ALSO

## COLOPHON

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

BUGS

SEE ALSO

COLOPHON

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

**#include
<math.h>**

**int
ilogb(double** *x***);
int ilogbf(float**

int ilogbl(long double

Link with
*−lm*.

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*

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*.

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 functions return **INT_MAX**.

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).

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

C99, POSIX.1-2001, POSIX.1-2008.

Before version 2.16, the following bugs existed in the glibc implementation of these functions:

* |
The domain error case where | ||

* |
The domain error case where |

**log**(3),
**logb**(3), **significand**(3)

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