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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25 .\" Modified 2002-07-27 by Walter Harms
26 .\" (walter.harms@informatik.uni-oldenburg.de)
27 .TH LOG1P 3 2010-09-20 "" "Linux Programmer's Manual"
29 log1p, log1pf, log1pl \- logarithm of 1 plus argument
34 .BI "double log1p(double " x );
36 .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 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
52 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
53 _POSIX_C_SOURCE\ >=\ 200112L;
62 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
63 _POSIX_C_SOURCE\ >=\ 200112L;
71 returns a value equivalent to
77 It is computed in a way
78 that is accurate even if the value of \fIx\fP is near zero.
80 On success, these functions return the natural logarithm of
90 is positive infinity, positive infinity is returned.
94 is \-1, a pole error occurs,
95 and the functions return
104 is less than \-1 (including negative infinity),
105 a domain error occurs,
106 and a NaN (not a number) is returned.
107 .\" POSIX.1 specifies a possible range error if x is subnormal
108 .\" glibc 2.8 doesn't do this
112 for information on how to determine whether an error has occurred
113 when calling these functions.
115 The following errors can occur:
117 Domain error: \fIx\fP is less than \-1
121 An invalid floating-point exception
125 Pole error: \fIx\fP is \-1
129 A divide-by-zero floating-point exception
133 These functions do not set
135 .\" FIXME . Is it intentional that these functions do not set errno?
136 .\" log(), log2(), log10() do set errno
137 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6792