ilogb - Man Page

Math library (libm, -lm)

#include <math.h>

int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);

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

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).

C11, POSIX.1-2008.

C99, POSIX.1-2001.

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.

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

logb(3), significand(3).

The man pages ilogbf(3) and ilogbl(3) are aliases of ilogb(3).