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 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
27 * Use is subject to license terms.
28 */
29
30 #pragma weak __logb = logb
31 #pragma weak _logb = logb
32
33 #include "libm.h"
34 #include "xpg6.h" /* __xpg6 */
35 #define _C99SUSv3_logb _C99SUSv3_logb_subnormal_is_like_ilogb
36
37 #if defined(__x86)
38 static const double two52 = 4503599627370496.0;
39 #else
40 /*
41 * v: high part of a non-zero subnormal |x|; w: low part of |x|
42 */
43 static int
ilogb_subnormal(unsigned v,unsigned w)44 ilogb_subnormal(unsigned v, unsigned w) {
45 int r = -1022 - 52;
46
47 if (v)
48 r += 32;
49 else
50 v = w;
51 if (v & 0xffff0000)
52 r += 16, v >>= 16;
53 if (v & 0xff00)
54 r += 8, v >>= 8;
55 if (v & 0xf0)
56 r += 4, v >>= 4;
57 v <<= 1;
58 return (r + ((0xffffaa50 >> v) & 0x3));
59 }
60 #endif /* defined(__x86) */
61
62 double
logb(double x)63 logb(double x) {
64 int *px = (int *) &x, k = px[HIWORD] & ~0x80000000;
65
66 if (k < 0x00100000) {
67 if ((px[LOWORD] | k) == 0)
68 return (_SVID_libm_err(x, x, 45));
69 else if ((__xpg6 & _C99SUSv3_logb) != 0) {
70 #if defined(__x86)
71 x *= two52;
72 return ((double) (((px[HIWORD] & 0x7ff00000) >> 20)
73 - 1075));
74 #else
75 return ((double) ilogb_subnormal(k, px[LOWORD]));
76 #endif
77 } else
78 return (-1022.0);
79 } else if (k < 0x7ff00000)
80 return ((double) ((k >> 20) - 1023));
81 else
82 return (x * x);
83 }
84