NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

VERSIONS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

## NAME

## SYNOPSIS

## DESCRIPTION

## RETURN VALUE

## ERRORS

## VERSIONS

## ATTRIBUTES

## CONFORMING TO

## SEE ALSO

## COLOPHON

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

VERSIONS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

log2, log2f, log2l − base-2 logarithmic function

**#include
<math.h>**

**double
log2(double** *x***);
float log2f(float**

long double log2l(long double

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*

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).

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)

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part of release 4.04 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
http://www.kernel.org/doc/man−pages/.

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