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 __scalbn = scalbn
30
31 #include "libm.h"
32
33 static const double
34 one = 1.0,
35 huge = 1.0e300,
36 tiny = 1.0e-300,
37 twom54 = 5.5511151231257827021181583404541015625e-17;
38
39 #if defined(__x86)
40 static const double two52 = 4503599627370496.0;
41 #else
42 /*
43 * Normalize non-zero subnormal x and return biased exponent of x in [-51,0]
44 */
45 static int
ilogb_biased(unsigned * px)46 ilogb_biased(unsigned *px) {
47 int s = 52;
48 unsigned v = px[HIWORD] & ~0x80000000, w = px[LOWORD], t = v;
49
50 if (t)
51 s -= 32;
52 else
53 t = w;
54 if (t & 0xffff0000)
55 s -= 16, t >>= 16;
56 if (t & 0xff00)
57 s -= 8, t >>= 8;
58 if (t & 0xf0)
59 s -= 4, t >>= 4;
60 t <<= 1;
61 s -= (0xffffaa50 >> t) & 0x3;
62 if (s < 32) {
63 v = (v << s) | w >> (32 - s);
64 w <<= s;
65 } else {
66 v = w << (s - 32);
67 w = 0;
68 }
69 px[HIWORD] = (px[HIWORD] & 0x80000000) | v;
70 px[LOWORD] = w;
71 return (1 - s);
72 }
73 #endif /* defined(__x86) */
74
75 double
scalbn(double x,int n)76 scalbn(double x, int n) {
77 int *px, ix, hx, k;
78
79 px = (int *)&x;
80 ix = px[HIWORD];
81 hx = ix & ~0x80000000;
82 k = hx >> 20;
83
84 if (k == 0x7ff) /* x is inf or NaN */
85 return (x * one);
86
87 if (k == 0) {
88 if ((hx | px[LOWORD]) == 0 || n == 0)
89 return (x);
90 #if defined(__x86)
91 x *= two52;
92 ix = px[HIWORD];
93 k = ((ix & ~0x80000000) >> 20) - 52;
94 #else
95 k = ilogb_biased((unsigned *)px);
96 ix = px[HIWORD];
97 #endif
98 /* now k is in the range -51..0 */
99 k += n;
100 if (k > n) /* integer overflow occurred */
101 k = -100;
102 } else {
103 /* k is in the range 1..1023 */
104 k += n;
105 if (k < n) /* integer overflow occurred */
106 k = 0x7ff;
107 }
108
109 if (k > 0x7fe)
110 return (huge * ((ix < 0)? -huge : huge));
111 if (k < 1) {
112 if (k <= -54)
113 return (tiny * ((ix < 0)? -tiny : tiny));
114 k += 54;
115 px[HIWORD] = (ix & ~0x7ff00000) | (k << 20);
116 return (x * twom54);
117 }
118 px[HIWORD] = (ix & ~0x7ff00000) | (k << 20);
119 return (x);
120 }
121