1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
|
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" 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 derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" References consulted:
.\" Linux libc source code
.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\" 386BSD man pages
.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 1995-08-14 by Arnt Gulbrandsen <agulbra@troll.no>
.\" Modified 2002-07-27 by Walter Harms
.\" (walter.harms@informatik.uni-oldenburg.de)
.\"
.TH LOG2 3 2007-07-26 "" "Linux Programmer's Manual"
.SH NAME
log2, log2f, log2l \- base-2 logarithmic function
.SH SYNOPSIS
.nf
.B #include <math.h>
.sp
.BI "double log2(double " x );
.br
.BI "float log2f(float " x );
.br
.BI "long double log2l(long double " x );
.fi
.sp
Link with \fI\-lm\fP.
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR log2 (),
.BR log2f (),
.BR log2l ():
_XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
.I cc\ -std=c99
.ad b
.SH DESCRIPTION
The
.BR log2 ()
function returns the base 2 logarithm of \fIx\fP.
.SH ERRORS
The
.BR log2 ()
function can return the following error:
.TP
.B EDOM
The argument \fIx\fP is negative.
.TP
.B ERANGE
The argument \fIx\fP is zero.
The log of zero is not defined
(minus infinity).
.SH "CONFORMING TO"
SVr4, 4.3BSD, C89.
The
.I float
and
.I "long double"
variants are C99 requirements.
.SH "SEE ALSO"
.BR cbrt (3),
.BR clog2 (3),
.BR sqrt (3)
|
