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