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/* * Mode: C++; tabwidth: 4; indenttabsmode: nil; cbasicoffset: 4 * */ 
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/* ***** BEGIN LICENSE BLOCK ***** 
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1 
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* 
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* The contents of this file are subject to the Mozilla Public License Version 
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* 1.1 (the "License"); you may not use this file except in compliance with 
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* the License. You may obtain a copy of the License at 
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* http://www.mozilla.org/MPL/ 
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* 
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* Software distributed under the License is distributed on an "AS IS" basis, 
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License 
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* for the specific language governing rights and limitations under the 
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* License. 
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* 
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* The Original Code is Mozilla Communicator client code, released 
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* March 31, 1998. 
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* 
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* The Initial Developer of the Original Code is 
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* Netscape Communications Corporation. 
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* Portions created by the Initial Developer are Copyright (C) 1998 
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* the Initial Developer. All Rights Reserved. 
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* 
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* Contributor(s): 
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* 
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* Alternatively, the contents of this file may be used under the terms of 
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* either of the GNU General Public License Version 2 or later (the "GPL"), 
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* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"), 
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* in which case the provisions of the GPL or the LGPL are applicable instead 
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* of those above. If you wish to allow use of your version of this file only 
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* under the terms of either the GPL or the LGPL, and not to allow others to 
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* use your version of this file under the terms of the MPL, indicate your 
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* decision by deleting the provisions above and replace them with the notice 
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* and other provisions required by the GPL or the LGPL. If you do not delete 
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* the provisions above, a recipient may use your version of this file under 
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* the terms of any one of the MPL, the GPL or the LGPL. 
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* 
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* ***** END LICENSE BLOCK ***** */ 
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#include "jsstddef.h" 
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#include "jsbit.h" 
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#include "jsutil.h" 
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/* 
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* Check that we can use js_bitscan_clz32 to implement JS_FLOOR_LOG2 and 
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* JS_FLOOR_LOG2W and js_bitscan_clz64 to implement JS_FLOOR_LOG2W on 64bit 
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* systems. 
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*/ 
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#ifdef JS_HAS_BUILTIN_BITSCAN32 
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JS_STATIC_ASSERT(sizeof(unsigned int) == sizeof(JSUint32)); 
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JS_STATIC_ASSERT_IF(JS_BYTES_PER_WORD == 4, 
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sizeof(unsigned int) == sizeof(JSUword)); 
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#endif 
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#ifdef JS_HAS_BUILTIN_BITSCAN64 
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JS_STATIC_ASSERT_IF(JS_BYTES_PER_WORD == 8, 
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sizeof(unsigned long long) == sizeof(JSUword)); 
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#endif 
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/* 
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* Compute the log of the least power of 2 greater than or equal to n 
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*/ 
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JS_PUBLIC_API(JSIntn) 
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JS_CeilingLog2(JSUint32 n) 
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{ 
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JSIntn log2; 
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JS_CEILING_LOG2(log2, n); 
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return log2; 
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} 
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/* 
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* Compute the log of the greatest power of 2 less than or equal to n. 
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* This really just finds the highest set bit in the word. 
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*/ 
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JS_PUBLIC_API(JSIntn) 
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JS_FloorLog2(JSUint32 n) 
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{ 
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JSIntn log2; 
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JS_FLOOR_LOG2(log2, n); 
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return log2; 
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} 
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/* 
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* js_FloorLog2wImpl has to be defined only for 64bit nonGCC case. 
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*/ 
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#if !defined(JS_HAS_BUILTIN_BITSCAN64) && JS_BYTES_PER_WORD == 8 
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JSUword 
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js_FloorLog2wImpl(JSUword n) 
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{ 
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JSUword log2, m; 
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JS_ASSERT(n != 0); 
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log2 = 0; 
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m = n >> 32; 
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if (m != 0) { n = m; log2 = 32; } 
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m = n >> 16; 
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if (m != 0) { n = m; log2 = 16; } 
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m = n >> 8; 
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if (m != 0) { n = m; log2 = 8; } 
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m = n >> 4; 
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if (m != 0) { n = m; log2 = 4; } 
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m = n >> 2; 
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if (m != 0) { n = m; log2 = 2; } 
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log2 = (n >> 1); 
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return log2; 
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} 
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#endif 