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)):

       _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


   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

   If x is zero, then a domain error  occurs,  and  the  functions  return

   If  x  is  a  NaN, then a domain error occurs, and the functions return

   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,  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).


   For  an  explanation  of  the  terms  used   in   this   section,   see

   Interface                    Attribute      Value   
   ilogb(), ilogbf(), ilogbl()  Thread safety  MT-Safe 


   C99, POSIX.1-2001, POSIX.1-2008.


   Before   version   2.16,  the  following  bugs  existed  in  the  glibc
   implementation 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.


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


   This page is part of release 4.09 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

                              2016-03-15                          ILOGB(3)


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