atanh.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 */
/*
* atanh(x)
* Code originated from 4.3bsd.
* Modified by K.C. Ng for SUN 4.0 libm.
* Method :
* 1 2x x
* atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
* 2 1 - x 1 - x
* Note: to guarantee atanh(-x) = -atanh(x), we use
* sign(x) |x|
* atanh(x) = ------- * log1p(2*-------).
* 2 1 - |x|
*
* Special cases:
* atanh(x) is NaN if |x| > 1 with signal;
* atanh(NaN) is that NaN with no signal;
* atanh(+-1) is +-INF with signal.
*/
/* INDENT ON */
#include "libm.h"
#include "libm_synonyms.h"
#include "libm_protos.h"
#include <math.h>
double
atanh(double x) {
double t;
if (isnan(x))
return (x * x); /* switched from x + x for Cheetah */
t = fabs(x);
if (t > 1.0)
if (t == 1.0)
t = t / (1.0 - t);
}