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

NAME

log2, log2f, log2l - base-2 logarithmic function

SYNOPSIS

#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():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
 
or cc -std=c99

DESCRIPTION

The log2() function returns 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).

ERRORS

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).

VERSIONS

These functions first appeared in glibc in version 2.1.

CONFORMING TO

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)

COLOPHON

This page is part of release 3.74 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.
2010-09-12