The Tor Browser / file comparison
comparison: xpcom/io/nsSegmentedBuffer.h
xpcom/io/nsSegmentedBuffer.h
- branch
- TOR_BUG_9701
- changeset 8
- 97036ab72558
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| -1:000000000000 | 0:7c854f16d394 |
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| 1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */ | |
| 2 /* This Source Code Form is subject to the terms of the Mozilla Public | |
| 3 * License, v. 2.0. If a copy of the MPL was not distributed with this | |
| 4 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ | |
| 5 | |
| 6 #ifndef nsSegmentedBuffer_h__ | |
| 7 #define nsSegmentedBuffer_h__ | |
| 8 | |
| 9 #include "nsIMemory.h" | |
| 10 | |
| 11 class nsSegmentedBuffer | |
| 12 { | |
| 13 public: | |
| 14 nsSegmentedBuffer() | |
| 15 : mSegmentSize(0), mMaxSize(0), | |
| 16 mSegmentArray(nullptr), | |
| 17 mSegmentArrayCount(0), | |
| 18 mFirstSegmentIndex(0), mLastSegmentIndex(0) {} | |
| 19 | |
| 20 ~nsSegmentedBuffer() { | |
| 21 Empty(); | |
| 22 } | |
| 23 | |
| 24 | |
| 25 nsresult Init(uint32_t segmentSize, uint32_t maxSize); | |
| 26 | |
| 27 char* AppendNewSegment(); // pushes at end | |
| 28 | |
| 29 // returns true if no more segments remain: | |
| 30 bool DeleteFirstSegment(); // pops from beginning | |
| 31 | |
| 32 // returns true if no more segments remain: | |
| 33 bool DeleteLastSegment(); // pops from beginning | |
| 34 | |
| 35 // Call Realloc() on last segment. This is used to reduce memory | |
| 36 // consumption when data is not an exact multiple of segment size. | |
| 37 bool ReallocLastSegment(size_t newSize); | |
| 38 | |
| 39 void Empty(); // frees all segments | |
| 40 | |
| 41 inline uint32_t GetSegmentCount() { | |
| 42 if (mFirstSegmentIndex <= mLastSegmentIndex) | |
| 43 return mLastSegmentIndex - mFirstSegmentIndex; | |
| 44 else | |
| 45 return mSegmentArrayCount + mLastSegmentIndex - mFirstSegmentIndex; | |
| 46 } | |
| 47 | |
| 48 inline uint32_t GetSegmentSize() { return mSegmentSize; } | |
| 49 inline uint32_t GetMaxSize() { return mMaxSize; } | |
| 50 inline uint32_t GetSize() { return GetSegmentCount() * mSegmentSize; } | |
| 51 | |
| 52 inline char* GetSegment(uint32_t indx) { | |
| 53 NS_ASSERTION(indx < GetSegmentCount(), "index out of bounds"); | |
| 54 int32_t i = ModSegArraySize(mFirstSegmentIndex + (int32_t)indx); | |
| 55 return mSegmentArray[i]; | |
| 56 } | |
| 57 | |
| 58 protected: | |
| 59 inline int32_t ModSegArraySize(int32_t n) { | |
| 60 uint32_t result = n & (mSegmentArrayCount - 1); | |
| 61 NS_ASSERTION(result == n % mSegmentArrayCount, | |
| 62 "non-power-of-2 mSegmentArrayCount"); | |
| 63 return result; | |
| 64 } | |
| 65 | |
| 66 inline bool IsFull() { | |
| 67 return ModSegArraySize(mLastSegmentIndex + 1) == mFirstSegmentIndex; | |
| 68 } | |
| 69 | |
| 70 protected: | |
| 71 uint32_t mSegmentSize; | |
| 72 uint32_t mMaxSize; | |
| 73 char** mSegmentArray; | |
| 74 uint32_t mSegmentArrayCount; | |
| 75 int32_t mFirstSegmentIndex; | |
| 76 int32_t mLastSegmentIndex; | |
| 77 }; | |
| 78 | |
| 79 // NS_SEGMENTARRAY_INITIAL_SIZE: This number needs to start out as a | |
| 80 // power of 2 given how it gets used. We double the segment array | |
| 81 // when we overflow it, and use that fact that it's a power of 2 | |
| 82 // to compute a fast modulus operation in IsFull. | |
| 83 // | |
| 84 // 32 segment array entries can accommodate 128k of data if segments | |
| 85 // are 4k in size. That seems like a reasonable amount that will avoid | |
| 86 // needing to grow the segment array. | |
| 87 #define NS_SEGMENTARRAY_INITIAL_COUNT 32 | |
| 88 | |
| 89 #endif // nsSegmentedBuffer_h__ |
