Copyright 1993 David Metcalfe (firstname.lastname@example.org) and Copyright 2008, Linux Foundation, written by Michael Kerrisk <email@example.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting ...
NAMElog2, 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():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTIONThese functions return the base 2 logarithm of x.
RETURN VALUEOn 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).
ERRORSSee 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).
VERSIONSThese functions first appeared in glibc in version 2.1.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
|log2(), log2f(), log2l()||Thread safety||MT-Safe|
CONFORMING TOC99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD.