log2 man page

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).

InterfaceAttributeValue
log2(), log2f(), log2l()Thread safetyMT-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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Referenced By

log(3), log10(3).

log2f(3) and log2l(3) are aliases of log2(3).

2016-03-15 Linux Programmer's Manual