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ILOGB(3) - man page online | library functions

Get integer exponent of a floating-point value.

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2015-04-19
ILOGB(3)                            Linux Programmer's Manual                            ILOGB(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 (see feature_test_macros(7)): ilogb(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99 ilogbf(), ilogbl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99
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 func‐ tions 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 │ └────────────────────────────┴───────────────┴─────────┘
CONFORMING TO C99, POSIX.1-2001, POSIX.1-2008.
BUGS Before version 2.16, the following bugs existed in the glibc implementation of these func‐ tions: * 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)
COLOPHON This page is part of release 4.04 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 http://www.kernel.org/doc/man-pages/.
2015-04-19 ILOGB(3)
This manual Reference Other manuals
ilogb(3) referred by logb(3) | significand(3)
refer to attributes(7) | feature_test_macros(7) | log(3) | logb(3) | math_error(7) | significand(3)