tanh.c revision 25c28e83beb90e7c80452a7c818c5e6f73a07dc8
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2011 Nexenta Systems, Inc. All rights reserved.
*/
/*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/* INDENT OFF */
/*
* TANH(X)
* RETURN THE HYPERBOLIC TANGENT OF X
* code based on 4.3bsd
* Modified by K.C. Ng for sun 4.0, Jan 31, 1987
*
* Method :
* 1. reduce x to non-negative by tanh(-x) = - tanh(x).
* 2.
* 0 < x <= 1.e-10 : tanh(x) := x
* -expm1(-2x)
* 1.e-10 < x <= 1 : tanh(x) := --------------
* expm1(-2x) + 2
* 2
* 1 <= x <= 22.0 : tanh(x) := 1 - ---------------
* expm1(2x) + 2
* 22.0 < x <= INF : tanh(x) := 1.
*
* Note: 22 was chosen so that fl(1.0+2/(expm1(2*22)+2)) == 1.
*
* Special cases:
* tanh(NaN) is NaN;
* only tanh(0)=0 is exact for finite argument.
*/
#include "libm.h"
#include "libm_synonyms.h"
#include "libm_protos.h"
#include <math.h>
static const double
one = 1.0,
two = 2.0,
small = 1.0e-10,
big = 1.0e10;
/* INDENT ON */
double
tanh(double x) {
double t, y, z;
int signx;
volatile double dummy;
if (isnan(x))
return (x * x); /* + -> * for Cheetah */
t = fabs(x);
z = one;
if (t <= 22.0) {
if (t > one)
else if (t > small) {
y = expm1(-t - t);
z = -y / (y + two);
} else {
/* raise the INEXACT flag for non-zero t */
#ifdef lint
#endif
return (x);
}
} else if (!finite(t))
return (copysign(1.0, x));
else
return (signx == 1 ? -z : z);
}