NAME

log2 - calculate the base-2 logarithm of a number

log2, log2f, log2l - base-2 logarithmic function

LIBRARY

Math library (libm, -lm)

#include <math.h>

double log2(double x);

#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)):

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

This function calculates the base-2 logarithm of x.

These functions return the base-2 logarithm of x.

This function returns, as a double, 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).

#include <math.h>
#include <stdio.h>

int main(void)
{
    printf("This is CS%i\n", (int) log2(1125899906842624));
}

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).

Interface	Attribute	Value
log2(), log2f(), log2l()	Thread safety	MT-Safe

C11, POSIX.1-2008.

glibc 2.1. C99, POSIX.1-2001.

The variant returning double also conforms to SVr4, 4.3BSD.