ilogb man page

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);

Link with -lm.

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

ilogb():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

ilogbf(), ilogbl():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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 functions 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).

InterfaceAttributeValue
ilogb(), ilogbf(), ilogbl()Thread safetyMT-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 functions:

*
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.

See Also

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

Colophon

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Referenced By

logb(3), significand(3).

ilogbf(3) and ilogbl(3) are aliases of ilogb(3).

2016-03-15 Linux Programmer's Manual