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
44static 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
60double
61exp2(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