log2 - calculate the base-2 logarithm of a number
log2, log2f, log2l - base-2 logarithmic function
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)):
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 |
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.