Name
ilogb, ilogbf, ilogbl - get integer exponent of a floating-point valueLibrary
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 toint
. Return Value
On success, these functions return the exponent ofx
, 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 |
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.
See Also
- log(3),
- logb(3),
- significand(3)