| 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). |
| • | 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. |
NAME
ilogb, ilogbf, ilogbl - get integer exponent of a floating-point value
LIBRARY
Math library (libm, -lm)
SYNOPSIS
#include <math.h>int ilogb(double \nx\n);\n
\nint ilogbf(float \nx\n);\n
\nint ilogbl(long double \nx\n);ilogb():
\n
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
\n
|| _XOPEN_SOURCE >= 500
\n
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEilogbf(), ilogbl():
\n
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
\n
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEDESCRIPTION
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, 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 |
| ilogb (), ilogbf (), ilogbl () | 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)