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ILOGB(3) Linux Programmer's Manual ILOGB(3)

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():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
 
or cc -std=c99
 
ilogbf(), ilogbl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
 
or cc -std=c99

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.
These functions do not set errno for this case.
Domain error: x is an infinity
These functions do not set errno or raise an exception for this case.

ATTRIBUTES

Multithreading (see pthreads(7))

The ilogb(), ilogbf(), and ilogbl() functions are thread-safe.

CONFORMING TO

C99, POSIX.1-2001.

SEE ALSO

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

COLOPHON

This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.
2013-08-06