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//===========================================================================
//
//      e_atanh.c
//
//      Part of the standard mathematical function library
//
//===========================================================================
// ####ECOSGPLCOPYRIGHTBEGIN####                                            
// -------------------------------------------                              
// This file is part of eCos, the Embedded Configurable Operating System.   
// Copyright (C) 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
//
// eCos is free software; you can redistribute it and/or modify it under    
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// for more details.                                                        
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//
// As a special exception, if other files instantiate templates or use      
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// General Public License v2.                                               
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// on this file might be covered by the GNU General Public License.         
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// ####ECOSGPLCOPYRIGHTEND####                                              
//===========================================================================
//#####DESCRIPTIONBEGIN####
//
// Author(s):   jlarmour
// Contributors:  jlarmour
// Date:        1998-02-13
// Purpose:     
// Description: 
// Usage:       
//
//####DESCRIPTIONEND####
//
//===========================================================================
 
// CONFIGURATION
 
#include <pkgconf/libm.h>   // Configuration header
 
// Include the Math library?
#ifdef CYGPKG_LIBM     
 
// Derived from code with the following copyright
 
 
/* @(#)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 "mathincl/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 = CYG_LIBM_HI(x);            /* high word */
        lx = CYG_LIBM_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 */
        CYG_LIBM_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;
}
 
#endif // ifdef CYGPKG_LIBM     
 
// EOF e_atanh.c