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//===========================================================================

//

//      s_tanh.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 Red Hat, Inc.

//

// eCos is free software; you can redistribute it and/or modify it under

// the terms of the GNU General Public License as published by the Free

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// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

// for more details.

//

// You should have received a copy of the GNU General Public License along

// with eCos; if not, write to the Free Software Foundation, Inc.,

// 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.

//

// As a special exception, if other files instantiate templates or use macros

// or inline functions from this file, or you compile this file and link it

// with other works to produce a work based on this file, this file does not

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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

/* @(#)s_tanh.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.

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

 */

/* Tanh(x)

 * Return the Hyperbolic Tangent of x

 *

 * Method :

 *                                     x    -x

 *                                    e  - e

 *      0. tanh(x) is defined to be -----------

 *                                     x    -x

 *                                    e  + e

 *      1. reduce x to non-negative by tanh(-x) = -tanh(x).

 *      2.  0      <= x <= 2**-55 : tanh(x) := x*(one+x)

 *                                              -t

 *          2**-55 <  x <=  1     : tanh(x) := -----; t = expm1(-2x)

 *                                             t + 2

 *                                                   2

 *          1      <= x <=  22.0  : tanh(x) := 1-  ----- ; t=expm1(2x)

 *                                                 t + 2

 *          22.0   <  x <= INF    : tanh(x) := 1.

 *

 * Special cases:

 *      tanh(NaN) is NaN;

 *      only tanh(0)=0 is exact for finite argument.

 */

#include "mathincl/fdlibm.h"

static const double one=1.0, two=2.0, tiny = 1.0e-300;

        double tanh(double x)

{

        double t,z;

        int jx,ix;

    /* High word of |x|. */

        jx = CYG_LIBM_HI(x);

        ix = jx&0x7fffffff;

    /* x is INF or NaN */

        if(ix>=0x7ff00000) {

            if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */

            else       return one/x-one;    /* tanh(NaN) = NaN */

        }

    /* |x| < 22 */

        if (ix < 0x40360000) {          /* |x|<22 */

            if (ix<0x3c800000)          /* |x|<2**-55 */

                return x*(one+x);       /* tanh(small) = small */

            if (ix>=0x3ff00000) {       /* |x|>=1  */

                t = expm1(two*fabs(x));

                z = one - two/(t+two);

            } else {

                t = expm1(-two*fabs(x));

                z= -t/(t+two);

            }

    /* |x| > 22, return +-1 */

        } else {

            z = one - tiny;             /* raised inexact flag */

        }

        return (jx>=0)? z: -z;

}

#endif // ifdef CYGPKG_LIBM     

// EOF s_tanh.c