ilogb(3)

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).
Interface | Attribute | Value
 | 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.

SEE ALSO
log(3), logb(3), significand(3)