/* derived from /netlib/fdlibm */ /* @(#)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" 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 = __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;}