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96 lines
3.1 KiB
C++
96 lines
3.1 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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*
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* The contents of this file are subject to the Netscape Public
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* License Version 1.1 (the "License"); you may not use this file
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* except in compliance with the License. You may obtain a copy of
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* the License at http://www.mozilla.org/NPL/
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*
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* Software distributed under the License is distributed on an "AS
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* IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
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* implied. See the License for the specific language governing
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* rights and limitations under the License.
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*
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* The Original Code is mozilla.org code.
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*
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* The Initial Developer of the Original Code is Netscape
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* Communications Corporation. Portions created by Netscape are
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* Copyright (C) 1998 Netscape Communications Corporation. All
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* Rights Reserved.
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*
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* Contributor(s):
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*/
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#ifndef nsSegmentedBuffer_h__
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#define nsSegmentedBuffer_h__
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#include "nsIAllocator.h"
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#include "prclist.h"
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class nsSegmentedBuffer
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{
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public:
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nsSegmentedBuffer();
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~nsSegmentedBuffer();
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nsresult Init(PRUint32 segmentSize, PRUint32 maxSize,
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nsIAllocator* allocator = nsnull);
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char* AppendNewSegment(); // pushes at end
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// returns true if no more segments remain:
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PRBool DeleteFirstSegment(); // pops from beginning
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void Empty(); // frees all segments
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PRUint32 GetSegmentCount() {
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if (mFirstSegmentIndex <= mLastSegmentIndex)
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return mLastSegmentIndex - mFirstSegmentIndex;
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else
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return mSegmentArrayCount + mLastSegmentIndex - mFirstSegmentIndex;
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}
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PRUint32 GetSegmentSize() { return mSegmentSize; }
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PRUint32 GetSize() { return GetSegmentCount() * mSegmentSize; }
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char* GetSegment(PRUint32 indx) {
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NS_ASSERTION(0 <= indx && indx < GetSegmentCount(),
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"index out of bounds");
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PRInt32 i = ModSegArraySize(mFirstSegmentIndex + (PRInt32)indx);
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return mSegmentArray[i];
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}
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protected:
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PRInt32 ModSegArraySize(PRInt32 n) {
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PRUint32 result = n & (mSegmentArrayCount - 1);
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NS_ASSERTION(result == n % mSegmentArrayCount,
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"non-power-of-2 mSegmentArrayCount");
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return result;
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}
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PRBool IsFull() {
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return ModSegArraySize(mLastSegmentIndex + 1) == mFirstSegmentIndex;
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}
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protected:
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PRUint32 mSegmentSize;
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PRUint32 mMaxSize;
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nsIAllocator* mSegAllocator;
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char** mSegmentArray;
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PRUint32 mSegmentArrayCount;
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PRInt32 mFirstSegmentIndex;
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PRInt32 mLastSegmentIndex;
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};
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// NS_SEGMENTARRAY_INITIAL_SIZE: This number needs to start out as a
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// power of 2 given how it gets used. We double the segment array
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// when we overflow it, and use that fact that it's a power of 2
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// to compute a fast modulus operation in IsFull.
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//
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// 32 segment array entries can accommodate 128k of data if segments
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// are 4k in size. That seems like a reasonable amount that will avoid
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// needing to grow the segment array.
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#define NS_SEGMENTARRAY_INITIAL_COUNT 32
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#endif // nsSegmentedBuffer_h__
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