getauxval.3: wfix

[thirdparty/man-pages.git] / man3 / log.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 1995-08-14 by Arnt Gulbrandsen <agulbra@troll.no>
.\" Modified 2002-07-27 by Walter Harms
.\" 	(walter.harms@informatik.uni-oldenburg.de)
.\"
.TH LOG 3  2015-04-19  "" "Linux Programmer's Manual"
.SH NAME
log, logf, logl \- natural logarithmic function
.SH SYNOPSIS
.nf
.B #include <math.h>
.sp
.BI "double log(double " x );
.br
.BI "float logf(float " x );
.br
.BI "long double logl(long double " x );
.fi
.sp
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 logf (),
.BR logl ():
.RS 4
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE\ >=\ 200112L;
.br
or
.I cc\ -std=c99
.RE
.ad
.SH DESCRIPTION
These functions return the natural logarithm of
.IR x .
.SH RETURN VALUE
On success, these functions return the natural logarithm of
.IR x .

If
.I x
is a NaN,
a NaN is returned.

If
.I x
is 1, the result is +0.

If
.I x
is positive infinity,
positive infinity is returned.

If
.I x
is zero,
then a pole error occurs, and the functions return
.RB - HUGE_VAL ,
.RB - HUGE_VALF ,
or
.RB - HUGE_VALL ,
respectively.

If
.I x
is negative (including negative infinity), then
a domain error occurs, and a NaN (not a number) is returned.
.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 negative
.I errno
is set to
.BR EDOM .
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.TP
Pole error: \fIx\fP is zero
.I errno
is set to
.BR ERANGE .
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;
lbw21 lb lb
l l l.
Interface	Attribute	Value
T{
.BR log (),
.BR logf (),
.BR logl ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.

The variant returning
.I double
also conforms to
SVr4, 4.3BSD, C89.
.SH BUGS
In glibc 2.5 and earlier,
taking the
.BR log ()
of a NaN produces a bogus invalid floating-point