usr/src/lib/libm/common/Q/exp2l.c

   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 __exp2l = exp2l
  31
  32 #include "libm.h"
  33 #include "longdouble.h"
  34
  35 /*
  36  *      exp2l(x) = 2**x = 2**((x-anint(x))+anint(x))
  37  *               = 2**anint(x)*2**(x-anint(x))
  38  *               = 2**anint(x)*exp((x-anint(x))*ln2)
  39  */
  40
  41 #define TINY    1.0e-20L        /* single: 1e-5, double: 1e-10, quad: 1e-20 */
  42 #define OVFLEXP 16400           /* single: 130,  double  1030,  quad: 16400 */
  43 #define UNFLEXP -16520          /* single:-155,  double -1080,  quad:-16520 */
  44
  45 static const long double
  46         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
  53         ovflexp = OVFLEXP,
  54         unflexp = UNFLEXP;
  55
  56 long double
  57 exp2l(long double x) {
  58         long double t;
  59
  60         if (!finitel(x)) {
  61                 if (isnanl(x) || x > zero)
  62                         return (x + x);
  63                 else
  64                         return (zero);
  65         }
  66         t = fabsl(x);
  67         if (t < half) {
  68                 if (t < tiny)
  69                         return (one + x);
  70                 else
  71                         return (expl(ln2 * x));
  72         }
  73         t = anintl(x);
  74         if (t < ovflexp) {
  75                 if (t >= unflexp)
  76                         return (scalbnl(expl(ln2 * (x - t)), (int) t));
  77                 else
  78                         return (scalbnl(one, unflexp)); /* underflow */
  79         } else
  80                 return (scalbnl(one, ovflexp)); /* overflow  */
  81 }