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 /*
  31  * arccosin function
  32  *                            ________
  33  *                           / 1 - x
  34  *      acos(x) = 2*atan2(  / -------- , 1 )
  35  *                        \/   1 + x
  36  *
  37  *                            ________
  38  *                           / 1 - x
  39  *              = 2*atan (  / -------- ) for non-exceptional x.
  40  *                        \/   1 + x
  41  *
  42  * Special cases:
  43  *      if x is NaN, return x itself;
  44  *      if |x|>1, return NaN with invalid signal.
  45  */
  46 
  47 #pragma weak acosl = __acosl
  48 
  49 #include "libm.h"
  50 
  51 static const long double zero = 0.0L, one = 1.0L;
  52 
  53 long double
  54 acosl(long double x) {
  55         if (isnanl(x))
  56                 return (x + x);
  57         else if (fabsl(x) < one)
  58                 x = atanl(sqrtl((one - x) / (one + x)));
  59         else if (x == -one)
  60                 x = atan2l(one, zero);  /* x <- PI */
  61         else if (x == one)
  62                 x = zero;
  63         else {          /* |x| > 1  create invalid signal */
  64                 return (zero / zero);
  65         }
  66         return (x + x);
  67 }