2f067034cd
__builtin_clz or count-leading-zeros. r=brendan git-svn-id: svn://10.0.0.236/trunk@190669 18797224-902f-48f8-a5cc-f745e15eee43
152 lines
6.9 KiB
C
152 lines
6.9 KiB
C
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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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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#ifndef jsbit_h___
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#define jsbit_h___
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#include "jstypes.h"
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#include "jsutil.h"
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JS_BEGIN_EXTERN_C
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/*
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** A jsbitmap_t is a long integer that can be used for bitmaps
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*/
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typedef JSUword jsbitmap_t; /* NSPR name, a la Unix system types */
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typedef jsbitmap_t jsbitmap; /* JS-style scalar typedef name */
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#define JS_TEST_BIT(_map,_bit) \
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((_map)[(_bit)>>JS_BITS_PER_WORD_LOG2] & (1L << ((_bit) & (JS_BITS_PER_WORD-1))))
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#define JS_SET_BIT(_map,_bit) \
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((_map)[(_bit)>>JS_BITS_PER_WORD_LOG2] |= (1L << ((_bit) & (JS_BITS_PER_WORD-1))))
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#define JS_CLEAR_BIT(_map,_bit) \
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((_map)[(_bit)>>JS_BITS_PER_WORD_LOG2] &= ~(1L << ((_bit) & (JS_BITS_PER_WORD-1))))
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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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extern JS_PUBLIC_API(JSIntn) JS_CeilingLog2(JSUint32 i);
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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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*/
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extern JS_PUBLIC_API(JSIntn) JS_FloorLog2(JSUint32 i);
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/*
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* Check if __builtin_clz is available which apeared first in GCC 3.4.
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* The built-in allows to speedup calculations of ceiling/floor log2,
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* see bug 327129.
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*/
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#if __GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
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# define JS_HAS_GCC_BUILTIN_CLZ
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#endif
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/*
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** Macro version of JS_CeilingLog2: Compute the log of the least power of
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** 2 greater than or equal to _n. The result is returned in _log2.
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*/
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#ifdef JS_HAS_GCC_BUILTIN_CLZ
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/*
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* Use __builtin_clz or count-leading-zeros to calculate ceil(log2(_n)).
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* The macro checks for "n <= 1" and not "n != 0" as __builtin_clz(0) is
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* undefined.
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*/
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# define JS_CEILING_LOG2(_log2,_n) \
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JS_BEGIN_MACRO \
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JS_STATIC_ASSERT(sizeof(unsigned int) == sizeof(JSUint32)); \
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unsigned int j_ = (unsigned int)(_n); \
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(_log2) = (j_ <= 1 ? 0 : 32 - __builtin_clz(j_ - 1)); \
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JS_END_MACRO
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#else
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# define JS_CEILING_LOG2(_log2,_n) \
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JS_BEGIN_MACRO \
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JSUint32 j_ = (JSUint32)(_n); \
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(_log2) = 0; \
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if ((j_) & ((j_)-1)) \
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(_log2) += 1; \
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if ((j_) >> 16) \
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(_log2) += 16, (j_) >>= 16; \
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if ((j_) >> 8) \
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(_log2) += 8, (j_) >>= 8; \
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if ((j_) >> 4) \
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(_log2) += 4, (j_) >>= 4; \
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if ((j_) >> 2) \
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(_log2) += 2, (j_) >>= 2; \
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if ((j_) >> 1) \
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(_log2) += 1; \
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JS_END_MACRO
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#endif
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/*
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** Macro version of JS_FloorLog2: Compute the log of the greatest power of
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** 2 less than or equal to _n. The result is returned in _log2.
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**
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** This is equivalent to finding the highest set bit in the word.
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*/
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#if JS_GCC_HAS_BUILTIN_CLZ
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/*
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* Use __builtin_clz or count-leading-zeros to calculate floor(log2(_n)).
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* Since __builtin_clz(0) is undefined, the macro set the loweset bit to 1
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* to ensure 0 result when _n == 0.
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*/
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# define JS_FLOOR_LOG2(_log2,_n) \
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JS_BEGIN_MACRO \
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JS_STATIC_ASSERT(sizeof(unsigned int) == sizeof(JSUint32)); \
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(_log2) = 31 - __builtin_clz(((unsigned int)(_n)) | 1); \
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JS_END_MACRO
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#else
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# define JS_FLOOR_LOG2(_log2,_n) \
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JS_BEGIN_MACRO \
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JSUint32 j_ = (JSUint32)(_n); \
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(_log2) = 0; \
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if ((j_) >> 16) \
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(_log2) += 16, (j_) >>= 16; \
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if ((j_) >> 8) \
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(_log2) += 8, (j_) >>= 8; \
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if ((j_) >> 4) \
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(_log2) += 4, (j_) >>= 4; \
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if ((j_) >> 2) \
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(_log2) += 2, (j_) >>= 2; \
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if ((j_) >> 1) \
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(_log2) += 1; \
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JS_END_MACRO
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#endif
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JS_END_EXTERN_C
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#endif /* jsbit_h___ */
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