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ilogb, ilogbf, ilogbl - get integer exponent of a floating-point value
#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
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.
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.
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. These functions do not set errno for this case. Domain error: x is an infinity These functions do not set errno or raise an exception for this case.
log(3), logb(3), significand(3)
This page is part of release 3.35 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://man7.org/linux/man- pages/. 2010-09-20 ILOGB(3)