LOG2(3) Linux Programmer's Manual LOG2(3)

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.

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)