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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():
       _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

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 functions 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 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.

SEE ALSO

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

COLOPHON

   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
   https://www.kernel.org/doc/man-pages/.

                              2016-03-15                          ILOGB(3)



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