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 #if defined(ELFOBJ)
  31 #pragma weak acoshl = __acoshl
  32 #endif
  33 
  34 #include "libm.h"
  35 
  36 static const long double
  37         zero    = 0.0L,
  38         ln2     = 6.931471805599453094172321214581765680755e-0001L,
  39         one     = 1.0L,
  40         big     = 1.e+20L;
  41 
  42 long double
  43 acoshl(long double x) {
  44         long double t;
  45 
  46         if (isnanl(x))
  47                 return (x + x);
  48         else if (x > big)
  49                 return (logl(x) + ln2);
  50         else if (x > one) {
  51                 t = sqrtl(x - one);
  52                 return (log1pl(t * (t + sqrtl(x + one))));
  53         } else if (x == one)
  54                 return (zero);
  55         else
  56                 return ((x - x) / (x - x));
  57 }