ILOGB(3)Linux Programmer's ManualILOGB(3)NAME ilogb, ilogbf, ilogbl - get integer exponent of a floating-point value SYNOPSIS #include <math.h> int ilogb(double x); int ilogbf(float x); int ilogbl(long double x); Link with -lm. Feature Test Macro Requirements for glibc (seefeature_test_macros(7)): ilogb(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE ilogbf(), ilogbl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 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 correspondinglogb(3)functions, cast to int. RETURN VALUE On success, these functions return the exponent of x, as a signed inte- ger. 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 Seemath_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, seeattributes(7). +----------------------------+---------------+---------+ |Interface | Attribute | Value | +----------------------------+---------------+---------+ |ilogb(), ilogbf(), ilogbl() | Thread safety | MT-Safe | +----------------------------+---------------+---------+ CONFORMING TO C99, POSIX.1-2001, POSIX.1-2008. BUGS Before version 2.16, the following bugs existed in the glibc implemen- tation 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 ALSOlog(3),logb(3),significand(3)COLOPHON This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. 2017-09-15ILOGB(3)