1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
3 .\" <mtk.manpages@gmail.com>
5 .\" Permission is granted to make and distribute verbatim copies of this
6 .\" manual provided the copyright notice and this permission notice are
7 .\" preserved on all copies.
9 .\" Permission is granted to copy and distribute modified versions of this
10 .\" manual under the conditions for verbatim copying, provided that the
11 .\" entire resulting derived work is distributed under the terms of a
12 .\" permission notice identical to this one.
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15 .\" manual page may be incorrect or out-of-date.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
16 .\" responsibility for errors or omissions, or for damages resulting from
17 .\" the use of the information contained herein. The author(s) may not
18 .\" have taken the same level of care in the production of this manual,
19 .\" which is licensed free of charge, as they might when working
22 .\" Formatted or processed versions of this manual, if unaccompanied by
23 .\" the source, must acknowledge the copyright and authors of this work.
25 .\" References consulted:
26 .\" Linux libc source code
27 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
29 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
30 .\" Modified 1995-08-14 by Arnt Gulbrandsen <agulbra@troll.no>
31 .\" Modified 2002-07-27 by Walter Harms
32 .\" (walter.harms@informatik.uni-oldenburg.de)
34 .TH LOG 3 2010-09-20 "" "Linux Programmer's Manual"
36 log, logf, logl \- natural logarithmic function
41 .BI "double log(double " x );
43 .BI "float logf(float " x );
45 .BI "long double logl(long double " x );
51 Feature Test Macro Requirements for glibc (see
52 .BR feature_test_macros (7)):
59 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
60 _POSIX_C_SOURCE\ >=\ 200112L;
69 function returns the natural logarithm of \fIx\fP.
71 On success, these functions return the natural logarithm of
81 is 1, the result is +0.
86 positive infinity is returned.
91 then a pole error occurs, and the functions return
100 is negative (including negative infinity), then
101 a domain error occurs, and a NaN (not a number) is returned.
105 for information on how to determine whether an error has occurred
106 when calling these functions.
108 The following errors can occur:
110 Domain error: \fIx\fP is negative
114 An invalid floating-point exception
118 Pole error: \fIx\fP is zero
122 A divide-by-zero floating-point exception
127 The variant returning
132 In glibc 2.5 and earlier,
135 of a NaN produces a bogus invalid floating-point