/* @(#)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"

#ifdef __STDC__

static const double one = 1.0, huge = 1e300;

#else

static double one = 1.0, huge = 1e300;

#endif

static double zero = 0.0;

#ifdef __STDC__

	double __ieee754_atanh(double x)

#else

	double __ieee754_atanh(x)

	double x;

#endif

{

	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;

}