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lightning-sunbird  0.9+nobinonly
jslog2.c
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00001 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
00002 /* ***** BEGIN LICENSE BLOCK *****
00003  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
00004  *
00005  * The contents of this file are subject to the Mozilla Public License Version
00006  * 1.1 (the "License"); you may not use this file except in compliance with
00007  * the License. You may obtain a copy of the License at
00008  * http://www.mozilla.org/MPL/
00009  *
00010  * Software distributed under the License is distributed on an "AS IS" basis,
00011  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
00012  * for the specific language governing rights and limitations under the
00013  * License.
00014  *
00015  * The Original Code is Mozilla Communicator client code, released
00016  * March 31, 1998.
00017  *
00018  * The Initial Developer of the Original Code is
00019  * Netscape Communications Corporation.
00020  * Portions created by the Initial Developer are Copyright (C) 1998
00021  * the Initial Developer. All Rights Reserved.
00022  *
00023  * Contributor(s):
00024  *
00025  * Alternatively, the contents of this file may be used under the terms of
00026  * either of the GNU General Public License Version 2 or later (the "GPL"),
00027  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
00028  * in which case the provisions of the GPL or the LGPL are applicable instead
00029  * of those above. If you wish to allow use of your version of this file only
00030  * under the terms of either the GPL or the LGPL, and not to allow others to
00031  * use your version of this file under the terms of the MPL, indicate your
00032  * decision by deleting the provisions above and replace them with the notice
00033  * and other provisions required by the GPL or the LGPL. If you do not delete
00034  * the provisions above, a recipient may use your version of this file under
00035  * the terms of any one of the MPL, the GPL or the LGPL.
00036  *
00037  * ***** END LICENSE BLOCK ***** */
00038 
00039 #include "jsstddef.h"
00040 #include "jsbit.h"
00041 #include "jsutil.h"
00042 
00043 /*
00044 ** Compute the log of the least power of 2 greater than or equal to n
00045 */
00046 JS_PUBLIC_API(JSIntn) JS_CeilingLog2(JSUint32 n)
00047 {
00048     JSIntn log2;
00049 
00050     JS_CEILING_LOG2(log2, n);
00051     return log2;
00052 }
00053 
00054 /*
00055 ** Compute the log of the greatest power of 2 less than or equal to n.
00056 ** This really just finds the highest set bit in the word.
00057 */
00058 JS_PUBLIC_API(JSIntn) JS_FloorLog2(JSUint32 n)
00059 {
00060     JSIntn log2;
00061 
00062     JS_FLOOR_LOG2(log2, n);
00063     return log2;
00064 }
00065 
00066 /*
00067  * js_FloorLog2wImpl has to be defined only for 64-bit non-GCC case.
00068  */
00069 #if !defined(JS_HAS_GCC_BUILTIN_CLZ) && JS_BYTES_PER_WORD == 8
00070 
00071 JSUword
00072 js_FloorLog2wImpl(JSUword n)
00073 {
00074     JSUword log2, m;
00075 
00076     JS_ASSERT(n != 0);
00077 
00078     log2 = 0;
00079     m = n >> 32;
00080     if (m != 0) { n = m; log2 = 32; }
00081     m = n >> 16;
00082     if (m != 0) { n = m; log2 |= 16; }
00083     m = n >> 8;
00084     if (m != 0) { n = m; log2 |= 8; }
00085     m = n >> 4;
00086     if (m != 0) { n = m; log2 |= 4; }
00087     m = n >> 2;
00088     if (m != 0) { n = m; log2 |= 2; }
00089     log2 |= (n >> 1);
00090 
00091     return log2;
00092 }
00093 
00094 #endif