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