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/* $OpenBSD: n_asinh.c,v 1.9 2009/04/11 20:03:21 martynas Exp $ */
/* $NetBSD: n_asinh.c,v 1.1 1995/10/10 23:36:35 ragge Exp $ */
/*
* Copyright (c) 1985, 1993
* The Regents of the University of California. 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.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
*/
#ifndef lint
static char sccsid[] = "@(#)asinh.c 8.1 (Berkeley) 6/4/93";
#endif /* not lint */
/* ASINH(X)
* RETURN THE INVERSE HYPERBOLIC SINE OF X
* DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
* CODED IN C BY K.C. NG, 2/16/85;
* REVISED BY K.C. NG on 3/7/85, 3/24/85, 4/16/85.
*
* Required system supported functions :
* copysign(x,y)
* sqrt(x)
*
* Required kernel function:
* log1p(x) ...return log(1+x)
*
* Method :
* Based on
* asinh(x) = sign(x) * log [ |x| + sqrt(x*x+1) ]
* we have
* asinh(x) := x if 1+x*x=1,
* := sign(x)*(log1p(x)+ln2)) if sqrt(1+x*x)=x, else
* := sign(x)*log1p(|x| + |x|/(1/|x| + sqrt(1+(1/|x|)^2)) )
*
* Accuracy:
* asinh(x) returns the exact inverse hyperbolic sine of x nearly rounded.
* In a test run with 52,000 random arguments on a VAX, the maximum
* observed error was 1.58 ulps (units in the last place).
*
* Constants:
* The hexadecimal values are the intended ones for the following constants.
* The decimal values may be used, provided that the compiler will convert
* from decimal to binary accurately enough to produce the hexadecimal values
* shown.
*/
#include "math.h"
#include "mathimpl.h"
static const double ln2hi = 6.9314718055829871446E-1;
static const double ln2lo = 1.6465949582897081279E-12;
double
asinh(double x)
{
double t,s;
static const double small=1.0E-10, /* fl(1+small*small) == 1 */
big =1.0E20, /* fl(1+big) == big */
one =1.0 ;
if (isnan(x))
return (x);
if((t=copysign(x,one))>small)
if(t<big) {
s=one/t; return(copysign(log1p(t+t/(s+sqrt(one+s*s))),x)); }
else /* if |x| > big */
{s=log1p(t)+ln2lo; return(copysign(s+ln2hi,x));}
else /* if |x| < small */
return(x);
}
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