/* atanh.c - math routines *//* Copyright 1992 Wind River Systems, Inc. *//*modification history--------------------01c,14oct92,jdi  made atanh() nomanual.01b,20sep92,smb  documentation additions01a,08jul92,smb  documentation.*//*DESCRIPTION* Copyright (c) 1985 Regents of the University of California.*  All rights reserved.** Redistribution and use in source and binary forms are permitted* provided that the above copyright notice and this paragraph are* duplicated in all such forms and that any documentation,* advertising materials, and other materials related to such* distribution and use acknowledge that the software was developed* by the University of California, Berkeley.  The name of the* University may not be used to endorse or promote products derived* from this software without specific prior written permission.* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.** All recipients should regard themselves as participants in an ongoing* research project and hence should feel obligated to report their* experiences (good or bad) with these elementary function codes, using* the sendbug(8) program, to the authors.*SEE ALSO: American National Standard X3.159-1989NOMANUAL*/#include "vxWorks.h"#include "math.h"#if defined(vax)||defined(tahoe)#include <errno.h>#endif	/* defined(vax)||defined(tahoe) *//******************************************************************************* atanh	-** ATANH(X)* RETURN THE HYPERBOLIC ARC TANGENT OF X* DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)* CODED IN C BY K.C. NG, 1/8/85;* REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85.** Required kernel function:* .CS*	log1p(x) 	...return log(1+x)* .CE** Method :* .CS*	Return*                          1              2x                          x*		atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)*                          2             1 - x                      1 - x* .CE** Special cases are if atanh(x) is NaN if |x| > 1 with signal; atanh(NaN) is * that NaN with no signal; or if atanh(+-1) is +-INF with signal.** atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded.* In a test run with 512,000 random arguments on a VAX, the maximum* observed error was 1.87 ulps (units in the last place) at* x= -3.8962076028810414000e-03.** NOMANUAL*/double atanh(x)double x;{	double copysign(),log1p(),z;	z = copysign(0.5,x);	x = copysign(x,1.0);#if defined(vax)||defined(tahoe)	if (x == 1.0) {	    extern double infnan();	    return(copysign(1.0,z)*infnan(ERANGE));	/* sign(x)*INF */	}#endif	/* defined(vax)||defined(tahoe) */	x = x/(1.0-x);	return( z*log1p(x+x) );}