1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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 ***** */
39 #include "jsstddef.h"
40 #include "jsbit.h"
42 /*
43 ** Compute the log of the least power of 2 greater than or equal to n
44 */
45 JS_PUBLIC_API(JSIntn) JS_CeilingLog2(JSUint32 n)
46 {
47 JSIntn log2 = 0;
49 if (n & (n-1))
50 log2++;
51 if (n >> 16)
52 log2 += 16, n >>= 16;
53 if (n >> 8)
54 log2 += 8, n >>= 8;
55 if (n >> 4)
56 log2 += 4, n >>= 4;
57 if (n >> 2)
58 log2 += 2, n >>= 2;
59 if (n >> 1)
60 log2++;
61 return log2;
62 }
64 /*
65 ** Compute the log of the greatest power of 2 less than or equal to n.
66 ** This really just finds the highest set bit in the word.
67 */
68 JS_PUBLIC_API(JSIntn) JS_FloorLog2(JSUint32 n)
69 {
70 JSIntn log2 = 0;
72 if (n >> 16)
73 log2 += 16, n >>= 16;
74 if (n >> 8)
75 log2 += 8, n >>= 8;
76 if (n >> 4)
77 log2 += 4, n >>= 4;
78 if (n >> 2)
79 log2 += 2, n >>= 2;
80 if (n >> 1)
81 log2++;
82 return log2;
83 }