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fea681da | 1 | .\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com> |
caba2e47 MK |
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 | .\" |
fea681da MK |
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16 | .\" manual page may be incorrect or out-of-date.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 | .\" Modified 2002-07-27 by Walter Harms | |
28 | .\" (walter.harms@informatik.uni-oldenburg.de) | |
fe0fefbf | 29 | .TH LOG1P 3 2015-03-02 "" "Linux Programmer's Manual" |
fea681da | 30 | .SH NAME |
9a2d673e | 31 | log1p, log1pf, log1pl \- logarithm of 1 plus argument |
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32 | .SH SYNOPSIS |
33 | .nf | |
34 | .B #include <math.h> | |
35 | .sp | |
36 | .BI "double log1p(double " x ); | |
d39541ec | 37 | .br |
fea681da | 38 | .BI "float log1pf(float " x ); |
d39541ec | 39 | .br |
fea681da | 40 | .BI "long double log1pl(long double " x ); |
c13182ef | 41 | .sp |
fea681da | 42 | .fi |
cc4615cc MK |
43 | Link with \fI\-lm\fP. |
44 | .sp | |
45 | .in -4n | |
46 | Feature Test Macro Requirements for glibc (see | |
47 | .BR feature_test_macros (7)): | |
48 | .in | |
49 | .sp | |
50 | .ad l | |
caba2e47 | 51 | .BR log1p (): |
1b5ffa62 MK |
52 | .RS 4 |
53 | _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 || | |
54 | _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE || | |
55 | _POSIX_C_SOURCE\ >=\ 200112L; | |
56 | .br | |
57 | or | |
caba2e47 | 58 | .I cc\ -std=c99 |
1b5ffa62 | 59 | .RE |
caba2e47 | 60 | .br |
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61 | .BR log1pf (), |
62 | .BR log1pl (): | |
1b5ffa62 MK |
63 | .RS 4 |
64 | _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE || | |
65 | _POSIX_C_SOURCE\ >=\ 200112L; | |
66 | .br | |
67 | or | |
cc4615cc | 68 | .I cc\ -std=c99 |
1b5ffa62 | 69 | .RE |
cc4615cc | 70 | .ad b |
fea681da | 71 | .SH DESCRIPTION |
5600f73a | 72 | These functions return a value equivalent to |
2d986c92 MK |
73 | .nf |
74 | ||
75 | log (1 + \fIx\fP) | |
76 | ||
77 | .fi | |
5600f73a | 78 | The result is computed in a way |
022671eb MK |
79 | that is accurate even if the value of |
80 | .I x | |
81 | is near zero. | |
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82 | .SH RETURN VALUE |
83 | On success, these functions return the natural logarithm of | |
84 | .IR "(1\ +\ x)" . | |
85 | ||
86 | If | |
87 | .I x | |
88 | is a NaN, | |
89 | a NaN is returned. | |
90 | ||
91 | If | |
92 | .I x | |
93 | is positive infinity, positive infinity is returned. | |
94 | ||
95 | If | |
96 | .I x | |
efe294cb | 97 | is \-1, a pole error occurs, |
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98 | and the functions return |
99 | .RB - HUGE_VAL , | |
100 | .RB - HUGE_VALF , | |
101 | or | |
102 | .RB - HUGE_VALL , | |
103 | respectively. | |
104 | ||
105 | If | |
106 | .I x | |
107 | is less than \-1 (including negative infinity), | |
efe294cb | 108 | a domain error occurs, |
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109 | and a NaN (not a number) is returned. |
110 | .\" POSIX.1 specifies a possible range error if x is subnormal | |
111 | .\" glibc 2.8 doesn't do this | |
112 | .SH ERRORS | |
113 | See | |
114 | .BR math_error (7) | |
115 | for information on how to determine whether an error has occurred | |
116 | when calling these functions. | |
117 | .PP | |
118 | The following errors can occur: | |
119 | .TP | |
120 | Domain error: \fIx\fP is less than \-1 | |
121 | .\" .I errno | |
122 | .\" is set to | |
123 | .\" .BR EDOM . | |
124 | An invalid floating-point exception | |
125 | .RB ( FE_INVALID ) | |
126 | is raised. | |
127 | .TP | |
128 | Pole error: \fIx\fP is \-1 | |
129 | .\" .I errno | |
130 | .\" is set to | |
131 | .\" .BR ERANGE . | |
132 | A divide-by-zero floating-point exception | |
133 | .RB ( FE_DIVBYZERO ) | |
134 | is raised. | |
135 | .PP | |
136 | These functions do not set | |
137 | .IR errno . | |
138 | .\" FIXME . Is it intentional that these functions do not set errno? | |
139 | .\" log(), log2(), log10() do set errno | |
140 | .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6792 | |
d05cb848 | 141 | .SH ATTRIBUTES |
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142 | For an explanation of the terms used in this section, see |
143 | .BR attributes (7). | |
144 | .TS | |
145 | allbox; | |
146 | lbw27 lb lb | |
147 | l l l. | |
148 | Interface Attribute Value | |
149 | T{ | |
d05cb848 PH |
150 | .BR log1p (), |
151 | .BR log1pf (), | |
d05cb848 | 152 | .BR log1pl () |
eb71cf70 MK |
153 | T} Thread safety MT-Safe |
154 | .TE | |
47297adb | 155 | .SH CONFORMING TO |
9a74e018 | 156 | C99, POSIX.1-2001, POSIX.1-2008. |
caba2e47 | 157 | .\" BSD |
47297adb | 158 | .SH SEE ALSO |
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159 | .BR exp (3), |
160 | .BR expm1 (3), | |
161 | .BR log (3) |