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fea681da | 1 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
5109fcf9 MK |
2 | .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk |
3 | .\" <mtk.manpages@gmail.com> | |
fea681da | 4 | .\" |
4b72fb64 | 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16 | .\" manual page may be incorrect or out-of-date.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 | .\" | |
50831f9b | 36 | .TH LOG 3 2010-09-20 "" "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> | |
42 | .sp | |
43 | .BI "double log(double " x ); | |
d39541ec | 44 | .br |
fea681da | 45 | .BI "float logf(float " x ); |
d39541ec | 46 | .br |
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47 | .BI "long double logl(long double " x ); |
48 | .fi | |
49 | .sp | |
20c58d70 | 50 | Link with \fI\-lm\fP. |
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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 logf (), | |
59 | .BR logl (): | |
b90c43a8 | 60 | .RS 4 |
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61 | _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE || |
62 | _POSIX_C_SOURCE\ >=\ 200112L; | |
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63 | .br |
64 | or | |
5109fcf9 | 65 | .I cc\ -std=c99 |
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66 | .RE |
67 | .ad | |
fea681da | 68 | .SH DESCRIPTION |
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69 | The |
70 | .BR log () | |
71 | function returns the natural logarithm of \fIx\fP. | |
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72 | .SH RETURN VALUE |
73 | On success, these functions return the natural logarithm of | |
74 | .IR x . | |
75 | ||
76 | If | |
77 | .I x | |
78 | is a NaN, | |
79 | a NaN is returned. | |
80 | ||
81 | If | |
82 | .I x | |
83 | is 1, the result is +0. | |
84 | ||
85 | If | |
86 | .I x | |
87 | is positive infinity, | |
88 | positive infinity is returned. | |
89 | ||
90 | If | |
91 | .I x | |
92 | is zero, | |
efe294cb | 93 | then a pole error occurs, and the functions return |
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94 | .RB - HUGE_VAL , |
95 | .RB - HUGE_VALF , | |
96 | or | |
97 | .RB - HUGE_VALL , | |
98 | respectively. | |
99 | ||
100 | If | |
101 | .I x | |
102 | is negative (including negative infinity), then | |
efe294cb | 103 | a domain error occurs, and a NaN (not a number) is returned. |
fea681da | 104 | .SH ERRORS |
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105 | See |
106 | .BR math_error (7) | |
107 | for information on how to determine whether an error has occurred | |
108 | when calling these functions. | |
109 | .PP | |
110 | The following errors can occur: | |
fea681da | 111 | .TP |
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112 | Domain error: \fIx\fP is negative |
113 | .I errno | |
114 | is set to | |
115 | .BR EDOM . | |
116 | An invalid floating-point exception | |
117 | .RB ( FE_INVALID ) | |
118 | is raised. | |
fea681da | 119 | .TP |
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120 | Pole error: \fIx\fP is zero |
121 | .I errno | |
122 | is set to | |
123 | .BR ERANGE . | |
124 | A divide-by-zero floating-point exception | |
125 | .RB ( FE_DIVBYZERO ) | |
126 | is raised. | |
47297adb | 127 | .SH CONFORMING TO |
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128 | C99, POSIX.1-2001. |
129 | The variant returning | |
130 | .I double | |
131 | also conforms to | |
68e1685c | 132 | SVr4, 4.3BSD, C89. |
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133 | .SH BUGS |
134 | In glibc 2.5 and earlier, | |
135 | taking the | |
136 | .BR log () | |
137 | of a NaN produces a bogus invalid floating-point | |