mirror of https://github.com/mkerrisk/man-pages
145 lines
3.5 KiB
Groff
145 lines
3.5 KiB
Groff
.\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com>
|
|
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
|
|
.\" <mtk.manpages@gmail.com>
|
|
.\"
|
|
.\" 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.\" manual page may be incorrect or out-of-date.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.
|
|
.\"
|
|
.\" Modified 2002-07-27 by Walter Harms
|
|
.\" (walter.harms@informatik.uni-oldenburg.de)
|
|
.TH LOG1P 3 2008-08-05 "" "Linux Programmer's Manual"
|
|
.SH NAME
|
|
log1p, log1pf, log1pl \- logarithm of 1 plus argument
|
|
.SH SYNOPSIS
|
|
.nf
|
|
.B #include <math.h>
|
|
.sp
|
|
.BI "double log1p(double " x );
|
|
.br
|
|
.BI "float log1pf(float " x );
|
|
.br
|
|
.BI "long double log1pl(long double " x );
|
|
.sp
|
|
.fi
|
|
Link with \fI\-lm\fP.
|
|
.sp
|
|
.in -4n
|
|
Feature Test Macro Requirements for glibc (see
|
|
.BR feature_test_macros (7)):
|
|
.in
|
|
.sp
|
|
.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
|
|
.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
|
|
.RE
|
|
.ad b
|
|
.SH DESCRIPTION
|
|
.I log1p(x)
|
|
returns a value equivalent to
|
|
.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.
|
|
.SH RETURN VALUE
|
|
On success, these functions return the natural logarithm of
|
|
.IR "(1\ +\ x)" .
|
|
|
|
If
|
|
.I x
|
|
is a NaN,
|
|
a NaN is returned.
|
|
|
|
If
|
|
.I x
|
|
is positive infinity, positive infinity is returned.
|
|
|
|
If
|
|
.I x
|
|
is \-1, a pole error occurs,
|
|
and the functions return
|
|
.RB - HUGE_VAL ,
|
|
.RB - HUGE_VALF ,
|
|
or
|
|
.RB - HUGE_VALL ,
|
|
respectively.
|
|
|
|
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 .
|
|
An invalid floating-point exception
|
|
.RB ( FE_INVALID )
|
|
is raised.
|
|
.TP
|
|
Pole error: \fIx\fP is \-1
|
|
.\" .I errno
|
|
.\" is set to
|
|
.\" .BR ERANGE .
|
|
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.
|
|
.\" BSD
|
|
.SH "SEE ALSO"
|
|
.BR exp (3),
|
|
.BR expm1 (3),
|
|
.BR log (3)
|