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 /*
  27  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  28  * Use is subject to license terms.
  29  */
  30 
  31 #pragma weak __acoshl = acoshl
  32 
  33 #include "libm.h"
  34 
  35 static const long double 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 {
  43         long double t;
  44 
  45         if (isnanl(x)) {
  46                 return (x + x);
  47         } else if (x > big) {
  48                 return (logl(x) + ln2);
  49         } else if (x > one) {
  50                 t = sqrtl(x - one);
  51                 return (log1pl(t * (t + sqrtl(x + one))));
  52         } else if (x == one) {
  53                 return (zero);
  54         } else {
  55                 return ((x - x) / (x - x));
  56         }
  57 }