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.\" $NetBSD: log.3,v 1.3 2011/09/13 08:51:32 wiz Exp $
.\"
.\" Copyright (c) 2011 Jukka Ruohonen <jruohonen@iki.fi>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd September 13, 2011
.Dt LOG 3
.Os
.Sh NAME
.Nm log ,
.Nm logf ,
.Nm log10 ,
.Nm log10f ,
.Nm log1p ,
.Nm log1pf
.Nm log2 ,
.Nm log2f ,
.Nd logarithm functions
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In math.h
.Ft double
.Fn log "double x"
.Ft float
.Fn logf "float x"
.Ft double
.Fn log10 "double x"
.Ft float
.Fn log10f "float x"
.Ft double
.Fn log1p "double x"
.Ft float
.Fn log1pf "float x"
.Ft double
.Fn log2 "double x"
.Ft float
.Fn log2f "float x"
.Sh DESCRIPTION
The following functions compute logarithms:
.Bl -bullet -offset 2n
.It
The
.Fn log
and
.Fn logf
functions return the natural logarithm.
.It
The
.Fn log10
and
.Fn log10f
functions return the base 10 logarithm.
.It
The
.Fn log1p
and
.Fn log1pf
functions return the natural logarithm of (1.0 +
.Fa x )
accurately even for very small values of
.Fa x .
.It
The
.Fn log2
and
.Fn log2f
functions return the base 2 logarithm.
.El
.Sh RETURN VALUES
Upon successful completion, the functions return the logarithm of
.Fa x
as descibed above.
Otherwise the following may occur:
.Bl -enum -offset indent
.It
If
.Fa x
is \*(Na, all functions return \*(Na.
.It
If
.Fa x
is positive infinity, all functions return
.Fa x .
If
.Fa x
is negative infinity, all functions return \*(Na.
.It
If
.Fa x
is +0.0 or -0.0, the
.Fn log ,
.Fn log10 ,
and
.Fn log2
families return either
.Dv -HUGE_VAL ,
.Dv -HUGE_VALF ,
or
.Dv -HUGE_VALL ,
whereas the
.Fn log1p
family returns
.Fa x .
.It
If
.Fa x
is +1.0, the
.Fn log ,
.Fn log10 ,
and
.Fn log2
families return +0.0.
If
.Fa x
is -1.0, the
.Fn log1p
family returns
.Dv -HUGE_VAL ,
.Dv -HUGE_VALF ,
or
.Dv -HUGE_VALL .
.El
.Pp
In addition, on a
.Tn VAX ,
.Va errno
is set to
.Er EDOM
and the reserved operand is returned
by
.Fn log
unless
.Fa x
\*[Gt] 0, by
.Fn log1p
unless
.Fa x
\*[Gt] \-1.
.Sh SEE ALSO
.Xr exp 3 ,
.Xr ilogb 3 ,
.Xr math 3
.Sh STANDARDS
The described functions conform to
.St -isoC-99 .
.Sh HISTORY
The history of the logarithm functions dates back to
.At v6 .
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