log2, log2f, log2l - base-2 logarithmic function

**#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

These functions return the base 2 logarithm of

*x*.

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).

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).

These functions first appeared in glibc in version 2.1.

For an explanation of the terms used in this section, see

**attributes**(7).

Interface |
Attribute |
Value |

log2 (), log2f (), log2l () |
Thread safety |
MT-Safe |

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning

*double* also conforms to SVr4, 4.3BSD.

**cbrt**(3),

**clog2**(3),

**log**(3),

**log10**(3),

**sqrt**(3)