xref: /titanic_51/usr/src/lib/libm/common/C/exp2.c (revision bf773d37f3253ade20599b1f3df2732d1b2ae424)
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
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