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

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Revision 460 - (hide annotations)
Sat Sep 26 23:15:22 2009 UTC (10 years, 9 months ago) by siliconforks
File size: 3427 byte(s)
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1 siliconforks 332 /* -*- 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 "jsstddef.h"
40     #include "jsbit.h"
41     #include "jsutil.h"
42    
43     /*
44 siliconforks 460 * 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 siliconforks 332 {
64     JSIntn log2;
65    
66     JS_CEILING_LOG2(log2, n);
67     return log2;
68     }
69    
70     /*
71 siliconforks 460 * 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 siliconforks 332 {
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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