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 * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
23 */
24 /*
25 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
26 * Use is subject to license terms.
27 */
28
29 #pragma weak __exp2 = exp2
30
31 /* INDENT OFF */
32 /*
33 * exp2(x)
34 * Code by K.C. Ng for SUN 4.0 libm.
35 * Method :
36 * exp2(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 /* INDENT ON */
41
42 #include "libm.h"
43
44 static const double C[] = {
45 0.0,
46 1.0,
47 0.5,
48 6.93147180559945286227e-01,
49 1.0e300,
50 1.0e-300,
51 };
52
53 #define zero C[0]
54 #define one C[1]
55 #define half C[2]
56 #define ln2 C[3]
57 #define huge C[4]
58 #define tiny C[5]
59
60 double
exp2(double x)61 exp2(double x) {
62 int ix, hx, k;
63 double t;
64
65 ix = ((int *)&x)[HIWORD];
66 hx = ix & ~0x80000000;
67
68 if (hx >= 0x4090e000) { /* |x| >= 1080 or x is nan */
69 if (hx >= 0x7ff00000) { /* x is inf or nan */
70 if (ix == 0xfff00000 && ((int *)&x)[LOWORD] == 0)
71 return (zero);
72 return (x * x);
73 }
74 t = (ix < 0)? tiny : huge;
75 return (t * t);
76 }
77
78 if (hx < 0x3fe00000) { /* |x| < 0.5 */
79 if (hx < 0x3c000000)
80 return (one + x);
81 return (exp(ln2 * x));
82 }
83
84 k = (int)x;
85 if (x != (double)k)
86 k = (int)((ix < 0)? x - half : x + half);
87 return (scalbn(exp(ln2 * (x - (double)k)), k));
88 }
89