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 __ilogb = ilogb
31
32 #include "libm.h"
33 #include "xpg6.h" /* __xpg6 */
34
35 #if defined(__x86)
36 static const double two52 = 4503599627370496.0;
37 #else
38 /*
39 * v: high part of a non-zero subnormal |x|; w: low part of |x|
40 */
41 static int
ilogb_subnormal(unsigned v,unsigned w)42 ilogb_subnormal(unsigned v, unsigned w) {
43 int r = -1022 - 52;
44
45 if (v)
46 r += 32;
47 else
48 v = w;
49 if (v & 0xffff0000)
50 r += 16, v >>= 16;
51 if (v & 0xff00)
52 r += 8, v >>= 8;
53 if (v & 0xf0)
54 r += 4, v >>= 4;
55 v <<= 1;
56 return (r + ((0xffffaa50 >> v) & 0x3));
57 }
58 #endif /* defined(__x86) */
59
60 static int
raise_invalid(int v)61 raise_invalid(int v) { /* SUSv3 requires ilogb(0,+/-Inf,NaN) raise invalid */
62 #ifndef lint
63 if ((__xpg6 & _C99SUSv3_ilogb_0InfNaN_raises_invalid) != 0) {
64 static const double zero = 0.0;
65 volatile double dummy __unused;
66
67 dummy = zero / zero;
68 }
69 #endif
70 return (v);
71 }
72
73 int
ilogb(double x)74 ilogb(double x) {
75 int *px = (int *) &x, k = px[HIWORD] & ~0x80000000;
76
77 if (k < 0x00100000) {
78 if ((px[LOWORD] | k) == 0)
79 return (raise_invalid(0x80000001));
80 else {
81 #if defined(__x86)
82 x *= two52;
83 return (((px[HIWORD] & 0x7ff00000) >> 20) - 1075);
84 #else
85 return (ilogb_subnormal(k, px[LOWORD]));
86 #endif
87 }
88 } else if (k < 0x7ff00000)
89 return ((k >> 20) - 1023);
90 else
91 return (raise_invalid(0x7fffffff));
92 }
93