LOG2(3)			   Linux Programmer's Manual		       LOG2(3)



NAME
       log2, log2f, log2l - base-2 logarithmic function

SYNOPSIS
       #include <math.h>

       double log2(double x);
       float log2f(float x);
       long double log2l(long double x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       log2(), log2f(), log2l():
	   _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       These functions return the base 2 logarithm of x.

RETURN VALUE
       On success, these functions return the base 2 logarithm of x.

       For  special  cases,  including where x is 0, 1, negative, infinity, or
       NaN, see log(3).

ERRORS
       See math_error(7) for information on how to determine whether an	 error
       has occurred when calling these functions.

       For  a discussion of the errors that can occur for these functions, see
       log(3).

VERSIONS
       These functions first appeared in glibc in version 2.1.

ATTRIBUTES
       For  an	explanation  of	 the  terms  used   in	 this	section,   see
       attributes(7).

       +-------------------------+---------------+---------+
       |Interface		 | Attribute	 | Value   |
       +-------------------------+---------------+---------+
       |log2(), log2f(), log2l() | Thread safety | MT-Safe |
       +-------------------------+---------------+---------+
CONFORMING TO
       C99, POSIX.1-2001, POSIX.1-2008.

       The variant returning double also conforms to SVr4, 4.3BSD.

SEE ALSO
       cbrt(3), clog2(3), log(3), log10(3), sqrt(3)

COLOPHON
       This  page  is  part of release 4.10 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			       LOG2(3)