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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14 .\" Since the Linux kernel and libraries are constantly changing, this
15 .\" manual page may be incorrect or out-of-date. The author(s) assume no
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19 .\" which is licensed free of charge, as they might when working
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25 .\" Modified 2002-07-27 by Walter Harms
26 .\" (walter.harms@informatik.uni-oldenburg.de)
27 .TH LOG1P 3 2008-08-05 "" "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)):
50 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 || _ISOC99_SOURCE; or
55 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
60 returns a value equivalent to
66 It is computed in a way
67 that is accurate even if the value of \fIx\fP is near zero.
69 On success, these functions return the natural logarithm of
79 is positive infinity, positive infinity is returned.
83 is \-1, a pole error occurs,
84 and the functions return
93 is less than \-1 (including negative infinity),
94 a domain error occurs,
95 and a NaN (not a number) is returned.
96 .\" POSIX.1 specifies a possible range error if x is subnormal
97 .\" glibc 2.8 doesn't do this
101 for information on how to determine whether an error has occurred
102 when calling these functions.
104 The following errors can occur:
106 Domain error: \fIx\fP is less than \-1
110 An invalid floating-point exception
114 Pole error: \fIx\fP is \-1
118 A divide-by-zero floating-point exception
122 These functions do not set
124 .\" FIXME . Is it intentional that these functions do not set errno?
125 .\" log(), log2(), log10() do set errno
126 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6792