/*

 * ====================================================

 * 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.

 * ====================================================

 *

 */

/* 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 "math_private.h"

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

static const double zero = 0.0;

double

__ieee754_atanh(double x)

{

  double t;

  int32_t hx,ix;

  u_int32_t lx;

  EXTRACT_WORDS(hx,lx,x);

  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 */

  SET_HIGH_WORD(x,ix);

  if(ix<0x3fe00000) {   /* x < 0.5 */

      t = x+x;

      t = 0.5*s_log1p(t+t*x/(one-x));

  } else 

      t = 0.5*s_log1p((x+x)/(one-x));

  if(hx>=0) return t; else return -t;

}