1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 
  22 /*
  23  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  24  */
  25 /*
  26  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  27  * Use is subject to license terms.
  28  */
  29 
  30 #pragma weak __atanhl = atanhl
  31 
  32 #include "libm.h"
  33 
  34 /*
  35  *                   1              2x                           x
  36  *      atanhl(x) = --- * LOG(1 + -------) = 0.5 * log1pl(2 * --------)
  37  *                   2             1 - x                       1 - x
  38  * Note: to guarantee atanhl(-x) = -atanhl(x), we use
  39  *                  sign(x)              |x|
  40  *      atanhl(x) = ------- * log1pl(2*-------).
  41  *                     2               1 - |x|
  42  *
  43  * Special cases:
  44  *      atanhl(x) is NaN if |x| > 1 with signal;
  45  *      atanhl(NaN) is that NaN with no signal;
  46  *      atanhl(+-1) is +-INF with signal.
  47  *
  48  */
  49 
  50 static const long double zero = 0.0L, half = 0.5L, one = 1.0L;
  51 
  52 long double
  53 atanhl(long double x) {
  54         long double t;
  55 
  56         t = fabsl(x);
  57         if (t == one)
  58                 return (x / zero);
  59         t = t / (one - t);
  60         return (copysignl(half, x) * log1pl(t + t));
  61 }