1 .\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com>
2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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27 .\" Modified 2002-07-27 by Walter Harms
28 .\" (walter.harms@informatik.uni-oldenburg.de)
29 .TH LOG1P 3 2017-09-15 "" "Linux Programmer's Manual"
31 log1p, log1pf, log1pl \- logarithm of 1 plus argument
36 .BI "double log1p(double " x );
37 .BI "float log1pf(float " x );
38 .BI "long double log1pl(long double " x );
44 Feature Test Macro Requirements for glibc (see
45 .BR feature_test_macros (7)):
51 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
52 || _XOPEN_SOURCE\ >=\ 500
53 .\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
54 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
55 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
61 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
62 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
63 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
67 These functions return a value equivalent to
73 The result is computed in a way
74 that is accurate even if the value of
78 On success, these functions return the natural logarithm of
88 is positive infinity, positive infinity is returned.
92 is \-1, a pole error occurs,
93 and the functions return
102 is less than \-1 (including negative infinity),
103 a domain error occurs,
104 and a NaN (not a number) is returned.
105 .\" POSIX.1 specifies a possible range error if x is subnormal
106 .\" glibc 2.8 doesn't do this
110 for information on how to determine whether an error has occurred
111 when calling these functions.
113 The following errors can occur:
115 Domain error: \fIx\fP is less than \-1
120 An invalid floating-point exception
124 Pole error: \fIx\fP is \-1
129 A divide-by-zero floating-point exception
133 For an explanation of the terms used in this section, see
139 Interface Attribute Value
144 T} Thread safety MT-Safe
147 C99, POSIX.1-2001, POSIX.1-2008.
150 Before version 2.22, the glibc implementation did not set
151 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
155 when a domain error occurred.
157 Before version 2.22, the glibc implementation did not set
158 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
162 when a range error occurred.