/* derived from /netlib/fdlibm */ /* @(#)e_atanh.c 1.3 95/01/18 *//* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunSoft, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice  * is preserved. * ==================================================== * */ /* __ieee754_atanh(x) * Method : *    1.Reduced x to positive by atanh(-x) = -atanh(x) *    2.For x>=0.5 *                  1              2x                          x *	atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------) *                  2             1 - x                      1 - x *	 * 	For x<0.5 *	atanh(x) = 0.5*log1p(2x+2x*x/(1-x)) * * Special cases: *	atanh(x) is NaN if |x| > 1 with signal; *	atanh(NaN) is that NaN with no signal; *	atanh(+-1) is +-INF with signal. * */ #include "fdlibm.h" static const double one = 1.0, Huge = 1e300; static double zero = 0.0; 	double __ieee754_atanh(double x){	double t;	int hx,ix;	unsigned lx;	hx = __HI(x);		/* high word */	lx = __LO(x);		/* low word */	ix = hx&0x7fffffff;	if ((ix|((lx|(-lx))>>31))>0x3ff00000) /* |x|>1 */	    return (x-x)/(x-x);	if(ix==0x3ff00000) 	    return x/zero;	if(ix<0x3e300000&&(Huge+x)>zero) return x;	/* x<2**-28 */	__HI(x) = ix;		/* x <- |x| */	if(ix<0x3fe00000) {		/* x < 0.5 */	    t = x+x;	    t = 0.5*log1p(t+t*x/(one-x));	} else 	    t = 0.5*log1p((x+x)/(one-x));	if(hx>=0) return t; else return -t;}