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 __exp2 = exp2
  32 
  33 
  34 /*
  35  * exp2(x)
  36  * Code by K.C. Ng for SUN 4.0 libm.
  37  * Method :
  38  *      exp2(x) = 2**x = 2**((x-anint(x))+anint(x))
  39  *              = 2**anint(x)*2**(x-anint(x))
  40  *              = 2**anint(x)*exp((x-anint(x))*ln2)
  41  */
  42 
  43 #include "libm.h"
  44 
  45 static const double C[] = {
  46         0.0,
  47         1.0,
  48         0.5,
  49         6.93147180559945286227e-01,
  50         1.0e300,
  51         1.0e-300,
  52 };
  53 
  54 #define zero            C[0]
  55 #define one             C[1]
  56 #define half            C[2]
  57 #define ln2             C[3]
  58 #define huge            C[4]
  59 #define tiny            C[5]
  60 
  61 double
  62 exp2(double x)
  63 {
  64         int ix, hx, k;
  65         double t;
  66 
  67         ix = ((int *)&x)[HIWORD];
  68         hx = ix & ~0x80000000;
  69 
  70         if (hx >= 0x4090e000) {              /* |x| >= 1080 or x is nan */
  71                 if (hx >= 0x7ff00000) {      /* x is inf or nan */
  72                         if (ix == 0xfff00000 && ((int *)&x)[LOWORD] == 0)
  73                                 return (zero);
  74 
  75                         return (x * x);
  76                 }
  77 
  78                 t = (ix < 0) ? tiny : huge;
  79                 return (t * t);
  80         }
  81 
  82         if (hx < 0x3fe00000) {               /* |x| < 0.5 */
  83                 if (hx < 0x3c000000)
  84                         return (one + x);
  85 
  86                 return (exp(ln2 * x));
  87         }
  88 
  89         k = (int)x;
  90 
  91         if (x != (double)k)
  92                 k = (int)((ix < 0) ? x - half : x + half);
  93 
  94         return (scalbn(exp(ln2 * (x - (double)k)), k));
  95 }