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**NAME**

ilogb, ilogbf, ilogbl - get integer exponent of a floating-point value

**SYNOPSIS**

#include<math.h>intilogb(doublex);intilogbf(floatx);intilogbl(longdoublex);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_SOURCEilogbf(),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 toint.

**RETURN** **VALUE**

On success, these functions return the exponent ofx, as a signed integer. Ifxis zero, then a domain error occurs, and the functions returnFP_ILOGB0. Ifxis a NaN, then a domain error occurs, and the functions returnFP_ILOGBNAN. Ifxis negative infinity or positive infinity, then a domain error occurs, and the functions returnINT_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:xis 0 or a NaN An invalid floating-point exception (FE_INVALID) is raised, anderrnois set toEDOM(but see BUGS). Domain error:xis an infinity An invalid floating-point exception (FE_INVALID) is raised, anderrnois set toEDOM(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 implementation of these functions: * The domain error case wherexis 0 or a NaN did not causeerrnoto be set or (on some architectures) raise a floating-point exception. * The domain error case wherexis an infinity did not causeerrnoto be set or raise a floating-point exception.

**SEE** **ALSO**

log(3),logb(3),significand(3)

**COLOPHON**

This page is part of release 5.01 of the Linuxman-pagesproject. 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/. 2017-09-15 ILOGB(3)