log2 - Man Page

base-2 logarithmic function


Math library (libm, -lm)


    #include <math.h>

double log2(double x);
float log2f(float x);
long double log2l(long double x);

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.

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).


For an explanation of the terms used in this section, see attributes(7).

log2(), log2f(), log2l()Thread safetyMT-Safe


C11, POSIX.1-2008.


glibc 2.1. C99, POSIX.1-2001.

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).

The man pages log2f(3) and log2l(3) are aliases of log2(3).

2023-10-31 Linux man-pages 6.06