Provided by: manpages-dev_3.35-0.1ubuntu1_all

**NAME**

log2, log2f, log2l - base-2 logarithmic function

**SYNOPSIS**

#include<math.h>doublelog2(doublex);floatlog2f(floatx);longdoublelog2l(longdoublex);Link with-lm. Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):log2(),log2f(),log2l(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; orcc-std=c99

**DESCRIPTION**

Thelog2() function returns the base 2 logarithm ofx.

**RETURN** **VALUE**

On success, these functions return the base 2 logarithm ofx. For special cases, including wherexis 0, 1, negative, infinity, or NaN, seelog(3).

**ERRORS**

Seemath_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, seelog(3).

**VERSIONS**

These functions first appeared in glibc in version 2.1.

**CONFORMING** **TO**

C99, POSIX.1-2001. The variant returningdoublealso conforms to SVr4, 4.3BSD.

**SEE** **ALSO**

cbrt(3),clog2(3),log(3),log10(3),sqrt(3)

**COLOPHON**

This page is part of release 3.35 of the Linuxman-pagesproject. A description of the project, and information about reporting bugs, can be found at http://man7.org/linux/man- pages/. 2010-09-12 LOG2(3)