/* @(#)s_tanh.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
* ====================================================
static char rcsid
[] = "$Id: s_tanh.c,v 1.3 1994/02/18 02:27:03 jtc Exp $";
* Return the Hyperbolic Tangent of x
* 0. tanh(x) is defined to be -----------
* 1. reduce x to non-negative by tanh(-x) = -tanh(x).
* 2. 0 <= x <= 2**-55 : tanh(x) := x*(one+x)
* 2**-55 < x <= 1 : tanh(x) := -----; t = expm1(-2x)
* 1 <= x <= 22.0 : tanh(x) := 1- ----- ; t=expm1(2x)
* 22.0 < x <= INF : tanh(x) := 1.
* only tanh(0)=0 is exact for finite argument.
static const double one
=1.0, two
=2.0, tiny
= 1.0e-300;
static double one
=1.0, two
=2.0, tiny
= 1.0e-300;
jx
= *( (((*(int*)&one
)>>29)^1) + (int*)&x
);
if (jx
>=0) return one
/x
+one
; /* tanh(+-inf)=+-1 */
else return one
/x
-one
; /* tanh(NaN) = NaN */
if (ix
< 0x40360000) { /* |x|<22 */
if (ix
<0x3c800000) /* |x|<2**-55 */
return x
*(one
+x
); /* tanh(small) = small */
if (ix
>=0x3ff00000) { /* |x|>=1 */
/* |x| > 22, return +-1 */
z
= one
- tiny
; /* raised inexact flag */