|
HTML rendering created 2026-05-30 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
|
|
|
ilogb(3) Library Functions Manual ilogb(3)
ilogb, ilogbf, ilogbl - get integer exponent of a floating-point
value
Math library (libm, -lm)
#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
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).
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโฌโโโโโโโโโโโโโโโโฌโโโโโโโโโโ
โ Interface โ Attribute โ Value โ
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโผโโโโโโโโโโโโโโโโผโโโโโโโโโโค
โ ilogb(), ilogbf(), ilogbl() โ Thread safety โ MT-Safe โ
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโดโโโโโโโโโโโโโโโโดโโโโโโโโโโ
C11, POSIX.1-2008.
C99, POSIX.1-2001.
Before glibc 2.16, the following bugs existed in the glibc
implementation of these functions:
โข 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.
โข 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)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
โจhttps://www.kernel.org/doc/man-pages/โฉ. If you have a bug report
for this manual page, see
โจhttps://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTINGโฉ.
This page was obtained from the tarball man-pages-6.18.tar.gz
fetched from
โจhttps://mirrors.edge.kernel.org/pub/linux/docs/man-pages/โฉ on
2026-05-24. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.18 2026-02-08 ilogb(3)
Pages that refer to this page: logb(3), significand(3)
|
HTML rendering created 2026-05-30 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
