php man page for log2

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 4.15 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/.

								    2017-09-15								   LOG2(3)