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LOG2

Section: Linux Programmer's Manual (3)
Updated: 2010-09-12
Index Return to Main Contents

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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 3.35 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://man7.org/linux/man-pages/.

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Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

VERSIONS

CONFORMING TO

SEE ALSO

COLOPHON

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