log2f

       #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():
           _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
           _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99

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 4.04 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2019 Hurricane Electric. All Rights Reserved.