.\" 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)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\" 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.\" manual page may be incorrect or out-of-date.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
.\" 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.
-.\"
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.\" 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 2002-07-27 "" "Linux Programmer's Manual"
+.TH LOG1P 3 2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
-log1p \- logarithm of 1 plus argument
+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
-Compile with \-std=c99; link with \-lm.
+Link with \fI\-lm\fP.
+.PP
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.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
-.BI log1p( x )
-returns a value equivalent to `log (1 + \fIx\fP)'. It is computed in a way
-that is accurate even if the value of \fIx\fP is near zero.
-.SH "CONFORMING TO"
-BSD, C99.
-The
-.I float
-and
-.I "long double"
-variants are C99 requirements.
-.SH "SEE ALSO"
+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)
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