michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef nsSegmentedBuffer_h__
michael@0: #define nsSegmentedBuffer_h__
michael@0: 
michael@0: #include "nsIMemory.h"
michael@0: 
michael@0: class nsSegmentedBuffer
michael@0: {
michael@0: public:
michael@0:     nsSegmentedBuffer()
michael@0:         : mSegmentSize(0), mMaxSize(0), 
michael@0:           mSegmentArray(nullptr),
michael@0:           mSegmentArrayCount(0),
michael@0:           mFirstSegmentIndex(0), mLastSegmentIndex(0) {}
michael@0: 
michael@0:     ~nsSegmentedBuffer() {
michael@0:         Empty();
michael@0:     }
michael@0: 
michael@0: 
michael@0:     nsresult Init(uint32_t segmentSize, uint32_t maxSize);
michael@0: 
michael@0:     char* AppendNewSegment();   // pushes at end
michael@0: 
michael@0:     // returns true if no more segments remain:
michael@0:     bool DeleteFirstSegment();  // pops from beginning
michael@0: 
michael@0:     // returns true if no more segments remain:
michael@0:     bool DeleteLastSegment();  // pops from beginning
michael@0: 
michael@0:     // Call Realloc() on last segment.  This is used to reduce memory
michael@0:     // consumption when data is not an exact multiple of segment size.
michael@0:     bool ReallocLastSegment(size_t newSize);
michael@0: 
michael@0:     void Empty();               // frees all segments
michael@0: 
michael@0:     inline uint32_t GetSegmentCount() {
michael@0:         if (mFirstSegmentIndex <= mLastSegmentIndex)
michael@0:             return mLastSegmentIndex - mFirstSegmentIndex;
michael@0:         else 
michael@0:             return mSegmentArrayCount + mLastSegmentIndex - mFirstSegmentIndex;
michael@0:     }
michael@0: 
michael@0:     inline uint32_t GetSegmentSize() { return mSegmentSize; }
michael@0:     inline uint32_t GetMaxSize() { return mMaxSize; }
michael@0:     inline uint32_t GetSize() { return GetSegmentCount() * mSegmentSize; }
michael@0: 
michael@0:     inline char* GetSegment(uint32_t indx) {
michael@0:         NS_ASSERTION(indx < GetSegmentCount(), "index out of bounds");
michael@0:         int32_t i = ModSegArraySize(mFirstSegmentIndex + (int32_t)indx);
michael@0:         return mSegmentArray[i];
michael@0:     }
michael@0: 
michael@0: protected:
michael@0:     inline int32_t ModSegArraySize(int32_t n) {
michael@0:         uint32_t result = n & (mSegmentArrayCount - 1);
michael@0:         NS_ASSERTION(result == n % mSegmentArrayCount,
michael@0:                      "non-power-of-2 mSegmentArrayCount");
michael@0:         return result;
michael@0:     }
michael@0: 
michael@0:    inline bool IsFull() {
michael@0:         return ModSegArraySize(mLastSegmentIndex + 1) == mFirstSegmentIndex;
michael@0:     }
michael@0: 
michael@0: protected:
michael@0:     uint32_t            mSegmentSize;
michael@0:     uint32_t            mMaxSize;
michael@0:     char**              mSegmentArray;
michael@0:     uint32_t            mSegmentArrayCount;
michael@0:     int32_t             mFirstSegmentIndex;
michael@0:     int32_t             mLastSegmentIndex;
michael@0: };
michael@0: 
michael@0: // NS_SEGMENTARRAY_INITIAL_SIZE: This number needs to start out as a
michael@0: // power of 2 given how it gets used. We double the segment array
michael@0: // when we overflow it, and use that fact that it's a power of 2 
michael@0: // to compute a fast modulus operation in IsFull.
michael@0: //
michael@0: // 32 segment array entries can accommodate 128k of data if segments
michael@0: // are 4k in size. That seems like a reasonable amount that will avoid
michael@0: // needing to grow the segment array.
michael@0: #define NS_SEGMENTARRAY_INITIAL_COUNT 32
michael@0: 
michael@0: #endif // nsSegmentedBuffer_h__