log2 man page

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():



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).


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).

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)

Referenced By

log(3), log10(3).

Explore man page connections for log2(3).

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