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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16 | .\" manual page may be incorrect or out-of-date.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 | .\" | |
4b8c67d9 | 36 | .TH LOG 3 2017-09-15 "" "Linux Programmer's Manual" |
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37 | .SH NAME |
38 | log, logf, logl \- natural logarithmic function | |
39 | .SH SYNOPSIS | |
40 | .nf | |
41 | .B #include <math.h> | |
68e4db0a | 42 | .PP |
fea681da | 43 | .BI "double log(double " x ); |
fea681da | 44 | .BI "float logf(float " x ); |
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45 | .BI "long double logl(long double " x ); |
46 | .fi | |
68e4db0a | 47 | .PP |
20c58d70 | 48 | Link with \fI\-lm\fP. |
68e4db0a | 49 | .PP |
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50 | .in -4n |
51 | Feature Test Macro Requirements for glibc (see | |
52 | .BR feature_test_macros (7)): | |
53 | .in | |
68e4db0a | 54 | .PP |
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55 | .ad l |
56 | .BR logf (), | |
57 | .BR logl (): | |
b90c43a8 | 58 | .RS 4 |
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59 | _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L |
60 | || /* Since glibc 2.19: */ _DEFAULT_SOURCE | |
61 | || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE | |
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62 | .RE |
63 | .ad | |
fea681da | 64 | .SH DESCRIPTION |
5600f73a | 65 | These functions return the natural logarithm of |
022671eb | 66 | .IR x . |
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67 | .SH RETURN VALUE |
68 | On success, these functions return the natural logarithm of | |
69 | .IR x . | |
847e0d88 | 70 | .PP |
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71 | If |
72 | .I x | |
73 | is a NaN, | |
74 | a NaN is returned. | |
847e0d88 | 75 | .PP |
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76 | If |
77 | .I x | |
78 | is 1, the result is +0. | |
847e0d88 | 79 | .PP |
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80 | If |
81 | .I x | |
82 | is positive infinity, | |
83 | positive infinity is returned. | |
847e0d88 | 84 | .PP |
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85 | If |
86 | .I x | |
87 | is zero, | |
efe294cb | 88 | then a pole error occurs, and the functions return |
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89 | .RB - HUGE_VAL , |
90 | .RB - HUGE_VALF , | |
91 | or | |
92 | .RB - HUGE_VALL , | |
93 | respectively. | |
847e0d88 | 94 | .PP |
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95 | If |
96 | .I x | |
97 | is negative (including negative infinity), then | |
efe294cb | 98 | a domain error occurs, and a NaN (not a number) is returned. |
fea681da | 99 | .SH ERRORS |
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100 | See |
101 | .BR math_error (7) | |
102 | for information on how to determine whether an error has occurred | |
103 | when calling these functions. | |
104 | .PP | |
105 | The following errors can occur: | |
fea681da | 106 | .TP |
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107 | Domain error: \fIx\fP is negative |
108 | .I errno | |
109 | is set to | |
110 | .BR EDOM . | |
111 | An invalid floating-point exception | |
112 | .RB ( FE_INVALID ) | |
113 | is raised. | |
fea681da | 114 | .TP |
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115 | Pole error: \fIx\fP is zero |
116 | .I errno | |
117 | is set to | |
118 | .BR ERANGE . | |
119 | A divide-by-zero floating-point exception | |
120 | .RB ( FE_DIVBYZERO ) | |
121 | is raised. | |
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122 | .SH ATTRIBUTES |
123 | For an explanation of the terms used in this section, see | |
124 | .BR attributes (7). | |
125 | .TS | |
126 | allbox; | |
34726473 | 127 | lbw21 lb lb |
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128 | l l l. |
129 | Interface Attribute Value | |
130 | T{ | |
131 | .BR log (), | |
132 | .BR logf (), | |
133 | .BR logl () | |
134 | T} Thread safety MT-Safe | |
135 | .TE | |
47297adb | 136 | .SH CONFORMING TO |
9a74e018 | 137 | C99, POSIX.1-2001, POSIX.1-2008. |
847e0d88 | 138 | .PP |
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139 | The variant returning |
140 | .I double | |
141 | also conforms to | |
68e1685c | 142 | SVr4, 4.3BSD, C89. |
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143 | .SH BUGS |
144 | In glibc 2.5 and earlier, | |
145 | taking the | |
146 | .BR log () | |
147 | of a NaN produces a bogus invalid floating-point | |