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ILOGB(3)                   Linux Programmer's Manual                  ILOGB(3)

       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 || _ISOC99_SOURCE; or cc -std=c99
       ilogbf(), ilogbl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; 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  func-

       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.

       C99, POSIX.1-2001.

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

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

                                  2009-02-04                          ILOGB(3)