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 __exp2l = exp2l
  32 
  33 #include "libm.h"
  34 #include "longdouble.h"
  35 
  36 /*
  37  *      exp2l(x) = 2**x = 2**((x-anint(x))+anint(x))
  38  *               = 2**anint(x)*2**(x-anint(x))
  39  *               = 2**anint(x)*exp((x-anint(x))*ln2)
  40  */
  41 
  42 #define TINY    1.0e-20L        /* single: 1e-5, double: 1e-10, quad: 1e-20 */
  43 #define OVFLEXP 16400           /* single: 130,  double  1030,  quad: 16400 */
  44 #define UNFLEXP -16520          /* single:-155,  double -1080,  quad:-16520 */
  45 
  46 static const long double zero = 0.0L,
  47         tiny = TINY * TINY,
  48         half = 0.5L,
  49         ln2 = 6.931471805599453094172321214581765680755e-0001L,
  50         one = 1.0L;
  51 
  52 static const int ovflexp = OVFLEXP, unflexp = UNFLEXP;
  53 
  54 long double
  55 exp2l(long double x)
  56 {
  57         long double t;
  58 
  59         if (!finitel(x)) {
  60                 if (isnanl(x) || x > zero)
  61                         return (x + x);
  62                 else
  63                         return (zero);
  64         }
  65 
  66         t = fabsl(x);
  67 
  68         if (t < half) {
  69                 if (t < tiny)
  70                         return (one + x);
  71                 else
  72                         return (expl(ln2 * x));
  73         }
  74 
  75         t = anintl(x);
  76 
  77         if (t < ovflexp) {
  78                 if (t >= unflexp)
  79                         return (scalbnl(expl(ln2 * (x - t)), (int)t));
  80                 else
  81                         return (scalbnl(one, unflexp));         /* underflow */
  82         } else {
  83                 return (scalbnl(one, ovflexp));                 /* overflow  */
  84         }
  85 }