/* @(#)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 "fdlibm.h"

#ifdef __STDC__

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

#else

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

#endif

#ifdef __STDC__

	double tanh(double x)

#else

	double tanh(x)

	double x;

#endif

{

	double t,z;

	int jx,ix;

    /* High word of |x|. */

	jx = __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;

}