log2 (3)

Leading comments

Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
    <mtk.manpages@gmail.com>

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(The comments found at the beginning of the groff file "man3/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

These functions return 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.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

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

CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD.

SEE ALSO

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

COLOPHON

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