ILOGB

Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
Index Return to Main Contents
 

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);

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

This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
BUGS
SEE ALSO
COLOPHON

This document was created by man2html, using the manual pages.
Time: 23:52:48 GMT, September 20, 2018