1 .\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com>
2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
3 .\" <mtk.manpages@gmail.com>
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27 .\" Modified 2002-07-27 by Walter Harms
28 .\" (walter.harms@informatik.uni-oldenburg.de)
29 .TH LOG1P 3 2021-03-22 "" "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)):
50 _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
51 || _XOPEN_SOURCE >= 500
52 .\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
53 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
54 || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
60 _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
61 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
62 || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
65 These functions return a value equivalent to
71 The result is computed in a way
72 that is accurate even if the value of
76 On success, these functions return the natural logarithm of
86 is positive infinity, positive infinity is returned.
90 is \-1, a pole error occurs,
91 and the functions return
100 is less than \-1 (including negative infinity),
101 a domain error occurs,
102 and a NaN (not a number) is returned.
103 .\" POSIX.1 specifies a possible range error if x is subnormal
104 .\" glibc 2.8 doesn't do this
108 for information on how to determine whether an error has occurred
109 when calling these functions.
111 The following errors can occur:
113 Domain error: \fIx\fP is less than \-1
118 An invalid floating-point exception
122 Pole error: \fIx\fP is \-1
127 A divide-by-zero floating-point exception
131 For an explanation of the terms used in this section, see
139 Interface Attribute Value
144 T} Thread safety MT-Safe
150 C99, POSIX.1-2001, POSIX.1-2008.
153 Before version 2.22, the glibc implementation did not set
154 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
158 when a domain error occurred.
160 Before version 2.22, the glibc implementation did not set
161 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
165 when a range error occurred.