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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 | .\" |
4b72fb64 | 5 | .\" %%%LICENSE_START(verbatim) |
fea681da MK |
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16 | .\" manual page may be incorrect or out-of-date.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 | .\" |
fea681da MK |
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 |
fea681da MK |
26 | .\" |
27 | .\" Modified 2002-07-27 by Walter Harms | |
28 | .\" (walter.harms@informatik.uni-oldenburg.de) | |
50831f9b | 29 | .TH LOG1P 3 2010-09-20 "" "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 (): |
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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 |
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72 | .I log1p(x) |
73 | returns a value equivalent to | |
74 | .nf | |
75 | ||
76 | log (1 + \fIx\fP) | |
77 | ||
78 | .fi | |
ca7b3c18 | 79 | It is computed in a way |
fea681da | 80 | that is accurate even if the value of \fIx\fP is near zero. |
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81 | .SH RETURN VALUE |
82 | On success, these functions return the natural logarithm of | |
83 | .IR "(1\ +\ x)" . | |
84 | ||
85 | If | |
86 | .I x | |
87 | is a NaN, | |
88 | a NaN is returned. | |
89 | ||
90 | If | |
91 | .I x | |
92 | is positive infinity, positive infinity is returned. | |
93 | ||
94 | If | |
95 | .I x | |
efe294cb | 96 | is \-1, a pole error occurs, |
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97 | and the functions return |
98 | .RB - HUGE_VAL , | |
99 | .RB - HUGE_VALF , | |
100 | or | |
101 | .RB - HUGE_VALL , | |
102 | respectively. | |
103 | ||
104 | If | |
105 | .I x | |
106 | is less than \-1 (including negative infinity), | |
efe294cb | 107 | a domain error occurs, |
caba2e47 MK |
108 | and a NaN (not a number) is returned. |
109 | .\" POSIX.1 specifies a possible range error if x is subnormal | |
110 | .\" glibc 2.8 doesn't do this | |
111 | .SH ERRORS | |
112 | See | |
113 | .BR math_error (7) | |
114 | for information on how to determine whether an error has occurred | |
115 | when calling these functions. | |
116 | .PP | |
117 | The following errors can occur: | |
118 | .TP | |
119 | Domain error: \fIx\fP is less than \-1 | |
120 | .\" .I errno | |
121 | .\" is set to | |
122 | .\" .BR EDOM . | |
123 | An invalid floating-point exception | |
124 | .RB ( FE_INVALID ) | |
125 | is raised. | |
126 | .TP | |
127 | Pole error: \fIx\fP is \-1 | |
128 | .\" .I errno | |
129 | .\" is set to | |
130 | .\" .BR ERANGE . | |
131 | A divide-by-zero floating-point exception | |
132 | .RB ( FE_DIVBYZERO ) | |
133 | is raised. | |
134 | .PP | |
135 | These functions do not set | |
136 | .IR errno . | |
137 | .\" FIXME . Is it intentional that these functions do not set errno? | |
138 | .\" log(), log2(), log10() do set errno | |
139 | .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6792 | |
47297adb | 140 | .SH CONFORMING TO |
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141 | C99, POSIX.1-2001. |
142 | .\" BSD | |
47297adb | 143 | .SH SEE ALSO |
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144 | .BR exp (3), |
145 | .BR expm1 (3), | |
146 | .BR log (3) |