text: /* @(#)e_atanh.c 5.1 93/09/24 */
  /*
   * ====================================================
   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   *
   * Developed at SunPro, a Sun Microsystems, Inc. business.
   * Permission to use, copy, modify, and distribute this
   * software is freely granted, provided that this notice
   * is preserved.
   * ====================================================
   */
  
  #if defined(LIBM_SCCS) && !defined(lint)
  static char rcsid[] = "$NetBSD: e_atanh.c,v 1.8 1995/05/10 20:44:55 jtc Exp $";
  #endif
  
  /* __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 "math.h"
  #include "math_private.h"
  
  #ifdef __STDC__
  static const double one = 1.0, huge = 1e300;
  #else
  static double one = 1.0, huge = 1e300;
  #endif
  
  #ifdef __STDC__
  static const double zero = 0.0;
  #else
  static double zero = 0.0;
  #endif
  
  #ifdef __STDC__
  	double __ieee754_atanh(double x)
  #else
  	double __ieee754_atanh(x)
  	double x;
  #endif
  {
  	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*log1p(t+t*x/(one-x));
  	} else
  	    t = 0.5*log1p((x+x)/(one-x));
  	if(hx>=0) return t; else return -t;
  }
  