1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/xpcom/io/nsSegmentedBuffer.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,89 @@
1.4 +/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
1.5 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.6 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.7 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.8 +
1.9 +#ifndef nsSegmentedBuffer_h__
1.10 +#define nsSegmentedBuffer_h__
1.11 +
1.12 +#include "nsIMemory.h"
1.13 +
1.14 +class nsSegmentedBuffer
1.15 +{
1.16 +public:
1.17 + nsSegmentedBuffer()
1.18 + : mSegmentSize(0), mMaxSize(0),
1.19 + mSegmentArray(nullptr),
1.20 + mSegmentArrayCount(0),
1.21 + mFirstSegmentIndex(0), mLastSegmentIndex(0) {}
1.22 +
1.23 + ~nsSegmentedBuffer() {
1.24 + Empty();
1.25 + }
1.26 +
1.27 +
1.28 + nsresult Init(uint32_t segmentSize, uint32_t maxSize);
1.29 +
1.30 + char* AppendNewSegment(); // pushes at end
1.31 +
1.32 + // returns true if no more segments remain:
1.33 + bool DeleteFirstSegment(); // pops from beginning
1.34 +
1.35 + // returns true if no more segments remain:
1.36 + bool DeleteLastSegment(); // pops from beginning
1.37 +
1.38 + // Call Realloc() on last segment. This is used to reduce memory
1.39 + // consumption when data is not an exact multiple of segment size.
1.40 + bool ReallocLastSegment(size_t newSize);
1.41 +
1.42 + void Empty(); // frees all segments
1.43 +
1.44 + inline uint32_t GetSegmentCount() {
1.45 + if (mFirstSegmentIndex <= mLastSegmentIndex)
1.46 + return mLastSegmentIndex - mFirstSegmentIndex;
1.47 + else
1.48 + return mSegmentArrayCount + mLastSegmentIndex - mFirstSegmentIndex;
1.49 + }
1.50 +
1.51 + inline uint32_t GetSegmentSize() { return mSegmentSize; }
1.52 + inline uint32_t GetMaxSize() { return mMaxSize; }
1.53 + inline uint32_t GetSize() { return GetSegmentCount() * mSegmentSize; }
1.54 +
1.55 + inline char* GetSegment(uint32_t indx) {
1.56 + NS_ASSERTION(indx < GetSegmentCount(), "index out of bounds");
1.57 + int32_t i = ModSegArraySize(mFirstSegmentIndex + (int32_t)indx);
1.58 + return mSegmentArray[i];
1.59 + }
1.60 +
1.61 +protected:
1.62 + inline int32_t ModSegArraySize(int32_t n) {
1.63 + uint32_t result = n & (mSegmentArrayCount - 1);
1.64 + NS_ASSERTION(result == n % mSegmentArrayCount,
1.65 + "non-power-of-2 mSegmentArrayCount");
1.66 + return result;
1.67 + }
1.68 +
1.69 + inline bool IsFull() {
1.70 + return ModSegArraySize(mLastSegmentIndex + 1) == mFirstSegmentIndex;
1.71 + }
1.72 +
1.73 +protected:
1.74 + uint32_t mSegmentSize;
1.75 + uint32_t mMaxSize;
1.76 + char** mSegmentArray;
1.77 + uint32_t mSegmentArrayCount;
1.78 + int32_t mFirstSegmentIndex;
1.79 + int32_t mLastSegmentIndex;
1.80 +};
1.81 +
1.82 +// NS_SEGMENTARRAY_INITIAL_SIZE: This number needs to start out as a
1.83 +// power of 2 given how it gets used. We double the segment array
1.84 +// when we overflow it, and use that fact that it's a power of 2
1.85 +// to compute a fast modulus operation in IsFull.
1.86 +//
1.87 +// 32 segment array entries can accommodate 128k of data if segments
1.88 +// are 4k in size. That seems like a reasonable amount that will avoid
1.89 +// needing to grow the segment array.
1.90 +#define NS_SEGMENTARRAY_INITIAL_COUNT 32
1.91 +
1.92 +#endif // nsSegmentedBuffer_h__
