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 __acoshl = acoshl
  31 
  32 #include "libm.h"
  33 
  34 static const long double
  35         zero    = 0.0L,
  36         ln2     = 6.931471805599453094172321214581765680755e-0001L,
  37         one     = 1.0L,
  38         big     = 1.e+20L;
  39 
  40 long double
  41 acoshl(long double x) {
  42         long double t;
  43 
  44         if (isnanl(x))
  45                 return (x + x);
  46         else if (x > big)
  47                 return (logl(x) + ln2);
  48         else if (x > one) {
  49                 t = sqrtl(x - one);
  50                 return (log1pl(t * (t + sqrtl(x + one))));
  51         } else if (x == one)
  52                 return (zero);
  53         else
  54                 return ((x - x) / (x - x));
  55 }