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);
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).
Interface |
Attribute |
Value |
ilogb (), ilogbf (), ilogbl () |
Thread safety |
MT-Safe |
C99, POSIX.1-2001, POSIX.1-2008.
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)