109 lines
2.9 KiB
C++
109 lines
2.9 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef nsSegmentedBuffer_h__
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#define nsSegmentedBuffer_h__
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#include "nsIMemory.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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: mSegmentSize(0)
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, mMaxSize(0)
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, mSegmentArray(nullptr)
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, mSegmentArrayCount(0)
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, mFirstSegmentIndex(0)
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, mLastSegmentIndex(0)
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{
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}
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~nsSegmentedBuffer()
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{
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Empty();
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}
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nsresult Init(uint32_t aSegmentSize, uint32_t aMaxSize);
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char* AppendNewSegment(); // pushes at end
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// returns true if no more segments remain:
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bool DeleteFirstSegment(); // pops from beginning
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// returns true if no more segments remain:
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bool DeleteLastSegment(); // pops from beginning
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// Call Realloc() on last segment. This is used to reduce memory
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// consumption when data is not an exact multiple of segment size.
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bool ReallocLastSegment(size_t aNewSize);
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void Empty(); // frees all segments
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inline uint32_t GetSegmentCount()
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{
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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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}
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inline uint32_t GetSegmentSize()
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{
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return mSegmentSize;
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}
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inline uint32_t GetMaxSize()
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{
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return mMaxSize;
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}
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inline uint32_t GetSize()
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{
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return GetSegmentCount() * mSegmentSize;
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}
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inline char* GetSegment(uint32_t aIndex)
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{
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NS_ASSERTION(aIndex < GetSegmentCount(), "index out of bounds");
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int32_t i = ModSegArraySize(mFirstSegmentIndex + (int32_t)aIndex);
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return mSegmentArray[i];
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}
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protected:
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inline int32_t ModSegArraySize(int32_t aIndex)
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{
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uint32_t result = aIndex & (mSegmentArrayCount - 1);
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NS_ASSERTION(result == aIndex % mSegmentArrayCount,
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"non-power-of-2 mSegmentArrayCount");
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return result;
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}
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inline bool IsFull()
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{
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return ModSegArraySize(mLastSegmentIndex + 1) == mFirstSegmentIndex;
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}
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protected:
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uint32_t mSegmentSize;
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uint32_t mMaxSize;
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char** mSegmentArray;
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uint32_t mSegmentArrayCount;
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int32_t mFirstSegmentIndex;
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int32_t 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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