/[jscoverage]/trunk/js/jslog2.cpp
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Contents of /trunk/js/jslog2.cpp

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Revision 507 - (show annotations)
Sun Jan 10 07:23:34 2010 UTC (9 years, 5 months ago) by siliconforks
File size: 3427 byte(s)
Update SpiderMonkey from Firefox 3.6rc1.

1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
2 /* ***** BEGIN LICENSE BLOCK *****
3 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
4 *
5 * The contents of this file are subject to the Mozilla Public License Version
6 * 1.1 (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 * http://www.mozilla.org/MPL/
9 *
10 * Software distributed under the License is distributed on an "AS IS" basis,
11 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
12 * for the specific language governing rights and limitations under the
13 * License.
14 *
15 * The Original Code is Mozilla Communicator client code, released
16 * March 31, 1998.
17 *
18 * The Initial Developer of the Original Code is
19 * Netscape Communications Corporation.
20 * Portions created by the Initial Developer are Copyright (C) 1998
21 * the Initial Developer. All Rights Reserved.
22 *
23 * Contributor(s):
24 *
25 * Alternatively, the contents of this file may be used under the terms of
26 * either of the GNU General Public License Version 2 or later (the "GPL"),
27 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
28 * in which case the provisions of the GPL or the LGPL are applicable instead
29 * of those above. If you wish to allow use of your version of this file only
30 * under the terms of either the GPL or the LGPL, and not to allow others to
31 * use your version of this file under the terms of the MPL, indicate your
32 * decision by deleting the provisions above and replace them with the notice
33 * and other provisions required by the GPL or the LGPL. If you do not delete
34 * the provisions above, a recipient may use your version of this file under
35 * the terms of any one of the MPL, the GPL or the LGPL.
36 *
37 * ***** END LICENSE BLOCK ***** */
38
39 #include "jsstdint.h"
40 #include "jsbit.h"
41 #include "jsutil.h"
42
43 /*
44 * Check that we can use js_bitscan_clz32 to implement JS_FLOOR_LOG2 and
45 * JS_FLOOR_LOG2W and js_bitscan_clz64 to implement JS_FLOOR_LOG2W on 64-bit
46 * systems.
47 */
48 #ifdef JS_HAS_BUILTIN_BITSCAN32
49 JS_STATIC_ASSERT(sizeof(unsigned int) == sizeof(JSUint32));
50 JS_STATIC_ASSERT_IF(JS_BYTES_PER_WORD == 4,
51 sizeof(unsigned int) == sizeof(JSUword));
52 #endif
53 #ifdef JS_HAS_BUILTIN_BITSCAN64
54 JS_STATIC_ASSERT_IF(JS_BYTES_PER_WORD == 8,
55 sizeof(unsigned long long) == sizeof(JSUword));
56 #endif
57
58 /*
59 * Compute the log of the least power of 2 greater than or equal to n
60 */
61 JS_PUBLIC_API(JSIntn)
62 JS_CeilingLog2(JSUint32 n)
63 {
64 JSIntn log2;
65
66 JS_CEILING_LOG2(log2, n);
67 return log2;
68 }
69
70 /*
71 * Compute the log of the greatest power of 2 less than or equal to n.
72 * This really just finds the highest set bit in the word.
73 */
74 JS_PUBLIC_API(JSIntn)
75 JS_FloorLog2(JSUint32 n)
76 {
77 JSIntn log2;
78
79 JS_FLOOR_LOG2(log2, n);
80 return log2;
81 }
82
83 /*
84 * js_FloorLog2wImpl has to be defined only for 64-bit non-GCC case.
85 */
86 #if !defined(JS_HAS_BUILTIN_BITSCAN64) && JS_BYTES_PER_WORD == 8
87
88 JSUword
89 js_FloorLog2wImpl(JSUword n)
90 {
91 JSUword log2, m;
92
93 JS_ASSERT(n != 0);
94
95 log2 = 0;
96 m = n >> 32;
97 if (m != 0) { n = m; log2 = 32; }
98 m = n >> 16;
99 if (m != 0) { n = m; log2 |= 16; }
100 m = n >> 8;
101 if (m != 0) { n = m; log2 |= 8; }
102 m = n >> 4;
103 if (m != 0) { n = m; log2 |= 4; }
104 m = n >> 2;
105 if (m != 0) { n = m; log2 |= 2; }
106 log2 |= (n >> 1);
107
108 return log2;
109 }
110
111 #endif

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