.\" 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.
.\"
.\" 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 2008-08-05 "" "Linux Programmer's Manual"
+.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>
-.sp
+.PP
.BI "double log1p(double " x );
-.br
.BI "float log1pf(float " x );
-.br
.BI "long double log1pl(long double " x );
-.sp
+.PP
.fi
Link with \fI\-lm\fP.
-.sp
+.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
-.sp
+.PP
.ad l
.BR log1p ():
.RS 4
-_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
-_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
-_POSIX_C_SOURCE\ >=\ 200112L;
-.br
-or
-.I cc\ -std=c99
+_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
-_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
-_POSIX_C_SOURCE\ >=\ 200112L;
-.br
-or
-.I cc\ -std=c99
+_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
-.I log1p(x)
-returns a value equivalent to
+These functions return a value equivalent to
+.PP
.nf
-
log (1 + \fIx\fP)
-
.fi
-It is computed in a way
-that is accurate even if the value of \fIx\fP is near zero.
+.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,
or
.RB - HUGE_VALL ,
respectively.
-
+.PP
If
.I x
is less than \-1 (including negative infinity),
The following errors can occur:
.TP
Domain error: \fIx\fP is less than \-1
-.\" .I errno
-.\" is set to
-.\" .BR EDOM .
+.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 .
+.I errno
+is set to
+.BR ERANGE
+(but see BUGS).
A divide-by-zero floating-point exception
.RB ( FE_DIVBYZERO )
is raised.
-.PP
-These functions do not set
-.IR errno .
-.\" FIXME . Is it intentional that these functions do not set errno?
-.\" log(), log2(), log10() do set errno
-.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6792
-.SH "CONFORMING TO"
-C99, POSIX.1-2001.
+.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 "SEE ALSO"
+.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)