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.\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com>
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" Modified 2002-07-27 by Walter Harms
.\" (walter.harms@informatik.uni-oldenburg.de)
.TH LOG1P 3 2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
log1p, log1pf, log1pl \- logarithm of 1 plus argument
.SH SYNOPSIS
.nf
.B #include <math.h>
.PP
.BI "double log1p(double " x );
.BI "float log1pf(float " x );
.BI "long double log1pl(long double " x );
.PP
.fi
Link with \fI\-lm\fP.
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.ad l
.BR log1p ():
.RS 4
_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
|| _XOPEN_SOURCE\ >=\ 500
.\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.br
.BR log1pf (),
.BR log1pl ():
.RS 4
_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.ad b
.SH DESCRIPTION
These functions return a value equivalent to
.PP
.nf
log (1 + \fIx\fP)
.fi
.PP
The result is computed in a way
that is accurate even if the value of
.I x
is near zero.
.SH RETURN VALUE
On success, these functions return the natural logarithm of
.IR "(1\ +\ x)" .
.PP
If
.I x
is a NaN,
a NaN is returned.
.PP
If
.I x
is positive infinity, positive infinity is returned.
.PP
If
.I x
is \-1, a pole error occurs,
and the functions return
.RB - HUGE_VAL ,
.RB - HUGE_VALF ,
or
.RB - HUGE_VALL ,
respectively.
.PP
If
.I x
is less than \-1 (including negative infinity),
a domain error occurs,
and a NaN (not a number) is returned.
.\" POSIX.1 specifies a possible range error if x is subnormal
.\" glibc 2.8 doesn't do this
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.PP
The following errors can occur:
.TP
Domain error: \fIx\fP is less than \-1
.I errno
is set to
.BR EDOM
(but see BUGS).
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.TP
Pole error: \fIx\fP is \-1
.I errno
is set to
.BR ERANGE
(but see BUGS).
A divide-by-zero floating-point exception
.RB ( FE_DIVBYZERO )
is raised.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw27 lb lb
l l l.
Interface Attribute Value
T{
.BR log1p (),
.BR log1pf (),
.BR log1pl ()
T} Thread safety MT-Safe
.TE
.SH CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
.\" BSD
.SH BUGS
Before version 2.22, the glibc implementation did not set
.\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
.I errno
to
.B EDOM
when a domain error occurred.
.PP
Before version 2.22, the glibc implementation did not set
.\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
.I errno
to
.B ERANGE
when a range error occurred.
.SH SEE ALSO
.BR exp (3),
.BR expm1 (3),
.BR log (3)
.SH COLOPHON
This page is part of release 5.09 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
|
