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NAME
ilogb, ilogbf, ilogbl - get integer exponent of a floating-point value
LIBRARY
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 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
C99, POSIX.1-2001, POSIX.1-2008.
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)