ilogbf(3) Linux Man Page - System Grab Bag

Name

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

Library

Math library ( libm ", " -lm )

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()

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

ilogbf() ilogbl()

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 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). allbox; lbx lb lb T{ ilogb()ilogbf()ilogbl()

Interface	Attribute	Value
T}	Thread safety	MT-Safe

Standards

C11, POSIX.1-2008.

History

C99, POSIX.1-2001.

Bugs

Before glibc 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.