gecko-dev/xpcom/io/nsSegmentedBuffer.h

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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*-
*
* The contents of this file are subject to the Netscape Public License
* Version 1.0 (the "NPL"); you may not use this file except in
* compliance with the NPL. You may obtain a copy of the NPL at
* http://www.mozilla.org/NPL/
*
* Software distributed under the NPL is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
* for the specific language governing rights and limitations under the
* NPL.
*
* The Initial Developer of this code under the NPL is Netscape
* Communications Corporation. Portions created by Netscape are
* Copyright (C) 1998 Netscape Communications Corporation. All Rights
* Reserved.
*/
#ifndef nsSegmentedBuffer_h__
#define nsSegmentedBuffer_h__
#include "nsIAllocator.h"
#include "prclist.h"
class nsSegmentedBuffer
{
public:
nsSegmentedBuffer();
~nsSegmentedBuffer();
nsresult Init(PRUint32 segmentSize, PRUint32 maxSize,
nsIAllocator* allocator = nsnull);
char* AppendNewSegment(); // pushes at end
// returns true if no more segments remain:
PRBool DeleteFirstSegment(); // pops from beginning
void Empty(); // frees all segments
PRUint32 GetSegmentCount() {
if (mFirstSegmentIndex <= mLastSegmentIndex)
return mLastSegmentIndex - mFirstSegmentIndex;
else
return mSegmentArrayCount + mLastSegmentIndex - mFirstSegmentIndex;
}
PRUint32 GetSegmentSize() { return mSegmentSize; }
PRUint32 GetSize() { return GetSegmentCount() * mSegmentSize; }
char* GetSegment(PRUint32 indx) {
NS_ASSERTION(0 <= indx && indx < GetSegmentCount(),
"index out of bounds");
PRInt32 i = ModSegArraySize(mFirstSegmentIndex + (PRInt32)indx);
return mSegmentArray[i];
}
protected:
PRInt32 ModSegArraySize(PRInt32 n) {
PRUint32 result = n & (mSegmentArrayCount - 1);
NS_ASSERTION(result == n % mSegmentArrayCount,
"non-power-of-2 mSegmentArrayCount");
return result;
}
PRBool IsFull() {
return ModSegArraySize(mLastSegmentIndex + 1) == mFirstSegmentIndex;
}
protected:
PRUint32 mSegmentSize;
PRUint32 mMaxSize;
nsIAllocator* mSegAllocator;
char** mSegmentArray;
PRUint32 mSegmentArrayCount;
PRInt32 mFirstSegmentIndex;
PRInt32 mLastSegmentIndex;
};
// NS_SEGMENTARRAY_INITIAL_SIZE: This number needs to start out as a
// power of 2 given how it gets used. We double the segment array
// when we overflow it, and use that fact that it's a power of 2
// to compute a fast modulus operation in IsFull.
//
// 32 segment array entries can accommodate 128k of data if segments
// are 4k in size. That seems like a reasonable amount that will avoid
// needing to grow the segment array.
#define NS_SEGMENTARRAY_INITIAL_COUNT 32
#endif // nsSegmentedBuffer_h__