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.\" Copyright (c) 2008-2010 David Schultz <das@FreeBSD.org>
.\" 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 AUTHOR 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 AUTHOR 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.
.\"
.\" $FreeBSD$
.\"
.Dd December 5, 2010
.Dt LOG 3
.Os
.Sh NAME
.Nm log ,
.Nm logf ,
.Nm logl ,
.Nm log10 ,
.Nm log10f ,
.Nm log2 ,
.Nm log2f ,
.Nm log1p ,
.Nm log1pf
.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 log2 "double x"
.Ft float
.Fn log2f "float x"
.Ft double
.Fn log1p "double x"
.Ft float
.Fn log1pf "float x"
.Sh DESCRIPTION
The
.Fn log
and
.Fn logf
functions compute the natural logarithm of
.Fa x .
.Pp
The
.Fn log10
and
.Fn log10f
functions compute the logarithm base 10 of
.Fa x ,
while
.Fn log2
and
.Fn log2f
compute the logarithm base 2 of
.Fa x .
.Pp
The
.Fn log1p
and
.Fn log1pf
functions compute the natural logarithm of
.No "1 + x" .
Computing the natural logarithm as
.Li log1p(x)
is more accurate than computing it as
.Li log(1 + x)
when
.Fa x
is close to zero.
.Sh RETURN VALUES
These functions return the requested logarithm; the logarithm of 1 is +0.
An attempt to take the logarithm of \*(Pm0 results in a divide-by-zero
exception, and -\*(If is returned.
Otherwise, attempting to take the logarithm of a negative number
results in an invalid exception and a return value of \*(Na.
.Sh SEE ALSO
.Xr exp 3 ,
.Xr ilogb 3 ,
.Xr math 3 ,
.Xr pow 3
.Sh STANDARDS
The
.Fn log ,
.Fn logf ,
.Fn log10 ,
.Fn log10f ,
.Fn log2 ,
.Fn log2f ,
.Fn log1p ,
and
.Fn log1pf
functions conform to
.St -isoC-99 .
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