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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

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     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)