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fea681da | 1 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
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2 | .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk |
3 | .\" <mtk.manpages@gmail.com> | |
fea681da | 4 | .\" |
93015253 | 5 | .\" %%%LICENSE_START(VERBATIM) |
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6 | .\" Permission is granted to make and distribute verbatim copies of this |
7 | .\" manual provided the copyright notice and this permission notice are | |
8 | .\" preserved on all copies. | |
9 | .\" | |
10 | .\" Permission is granted to copy and distribute modified versions of this | |
11 | .\" manual under the conditions for verbatim copying, provided that the | |
12 | .\" entire resulting derived work is distributed under the terms of a | |
13 | .\" permission notice identical to this one. | |
c13182ef | 14 | .\" |
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15 | .\" Since the Linux kernel and libraries are constantly changing, this |
16 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
17 | .\" responsibility for errors or omissions, or for damages resulting from | |
18 | .\" the use of the information contained herein. The author(s) may not | |
19 | .\" have taken the same level of care in the production of this manual, | |
20 | .\" which is licensed free of charge, as they might when working | |
21 | .\" professionally. | |
c13182ef | 22 | .\" |
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23 | .\" Formatted or processed versions of this manual, if unaccompanied by |
24 | .\" the source, must acknowledge the copyright and authors of this work. | |
4b72fb64 | 25 | .\" %%%LICENSE_END |
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26 | .\" |
27 | .\" References consulted: | |
28 | .\" Linux libc source code | |
29 | .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) | |
30 | .\" 386BSD man pages | |
31 | .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu) | |
32 | .\" Modified 1995-08-14 by Arnt Gulbrandsen <agulbra@troll.no> | |
33 | .\" Modified 2002-07-27 by Walter Harms | |
34 | .\" (walter.harms@informatik.uni-oldenburg.de) | |
35 | .\" | |
fe0fefbf | 36 | .TH LOG2 3 2015-03-02 "" "Linux Programmer's Manual" |
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37 | .SH NAME |
38 | log2, log2f, log2l \- base-2 logarithmic function | |
39 | .SH SYNOPSIS | |
40 | .nf | |
41 | .B #include <math.h> | |
42 | .sp | |
43 | .BI "double log2(double " x ); | |
44 | .br | |
45 | .BI "float log2f(float " x ); | |
46 | .br | |
47 | .BI "long double log2l(long double " x ); | |
48 | .fi | |
49 | .sp | |
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50 | Link with \fI\-lm\fP. |
51 | .sp | |
52 | .in -4n | |
53 | Feature Test Macro Requirements for glibc (see | |
54 | .BR feature_test_macros (7)): | |
55 | .in | |
56 | .sp | |
57 | .ad l | |
58 | .BR log2 (), | |
59 | .BR log2f (), | |
60 | .BR log2l (): | |
9fefcdd8 | 61 | .RS 4 |
f5fbd558 | 62 | _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L; |
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63 | .br |
64 | or | |
cc4615cc | 65 | .I cc\ -std=c99 |
9fefcdd8 | 66 | .RE |
cc4615cc | 67 | .ad b |
fea681da | 68 | .SH DESCRIPTION |
5600f73a | 69 | These functions return the base 2 logarithm of |
022671eb | 70 | .IR x . |
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71 | .SH RETURN VALUE |
72 | On success, these functions return the base 2 logarithm of | |
73 | .IR x . | |
74 | ||
75 | For special cases, including where | |
76 | .I x | |
77 | is 0, 1, negative, infinity, or NaN, see | |
78 | .BR log (3). | |
fea681da | 79 | .SH ERRORS |
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80 | See |
81 | .BR math_error (7) | |
82 | for information on how to determine whether an error has occurred | |
83 | when calling these functions. | |
84 | ||
85 | For a discussion of the errors that can occur for these functions, see | |
86 | .BR log (3). | |
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87 | .SH VERSIONS |
88 | These functions first appeared in glibc in version 2.1. | |
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89 | .SH ATTRIBUTES |
90 | For an explanation of the terms used in this section, see | |
91 | .BR attributes (7). | |
92 | .TS | |
93 | allbox; | |
94 | lbw24 lb lb | |
95 | l l l. | |
96 | Interface Attribute Value | |
97 | T{ | |
98 | .BR log2 (), | |
99 | .BR log2f (), | |
100 | .BR log2l () | |
101 | T} Thread safety MT-Safe | |
102 | .TE | |
47297adb | 103 | .SH CONFORMING TO |
9a74e018 | 104 | C99, POSIX.1-2001, POSIX.1-2008. |
e05e3635 | 105 | |
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106 | The variant returning |
107 | .I double | |
108 | also conforms to | |
3c78ebef | 109 | SVr4, 4.3BSD. |
47297adb | 110 | .SH SEE ALSO |
fea681da | 111 | .BR cbrt (3), |
36268806 | 112 | .BR clog2 (3), |
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113 | .BR log (3), |
114 | .BR log10 (3), | |
fea681da | 115 | .BR sqrt (3) |