/src/mozilla-central/xpcom/io/nsSegmentedBuffer.h
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1 | | /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ |
2 | | /* vim: set ts=8 sts=2 et sw=2 tw=80: */ |
3 | | /* This Source Code Form is subject to the terms of the Mozilla Public |
4 | | * License, v. 2.0. If a copy of the MPL was not distributed with this |
5 | | * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ |
6 | | |
7 | | #ifndef nsSegmentedBuffer_h__ |
8 | | #define nsSegmentedBuffer_h__ |
9 | | |
10 | | class nsSegmentedBuffer |
11 | | { |
12 | | public: |
13 | | nsSegmentedBuffer() |
14 | | : mSegmentSize(0) |
15 | | , mMaxSize(0) |
16 | | , mSegmentArray(nullptr) |
17 | | , mSegmentArrayCount(0) |
18 | | , mFirstSegmentIndex(0) |
19 | | , mLastSegmentIndex(0) |
20 | 0 | { |
21 | 0 | } |
22 | | |
23 | | ~nsSegmentedBuffer() |
24 | 0 | { |
25 | 0 | Empty(); |
26 | 0 | } |
27 | | |
28 | | |
29 | | nsresult Init(uint32_t aSegmentSize, uint32_t aMaxSize); |
30 | | |
31 | | char* AppendNewSegment(); // pushes at end |
32 | | |
33 | | // returns true if no more segments remain: |
34 | | bool DeleteFirstSegment(); // pops from beginning |
35 | | |
36 | | // returns true if no more segments remain: |
37 | | bool DeleteLastSegment(); // pops from beginning |
38 | | |
39 | | // Call Realloc() on last segment. This is used to reduce memory |
40 | | // consumption when data is not an exact multiple of segment size. |
41 | | bool ReallocLastSegment(size_t aNewSize); |
42 | | |
43 | | void Empty(); // frees all segments |
44 | | |
45 | | inline uint32_t GetSegmentCount() |
46 | 0 | { |
47 | 0 | if (mFirstSegmentIndex <= mLastSegmentIndex) { |
48 | 0 | return mLastSegmentIndex - mFirstSegmentIndex; |
49 | 0 | } else { |
50 | 0 | return mSegmentArrayCount + mLastSegmentIndex - mFirstSegmentIndex; |
51 | 0 | } |
52 | 0 | } |
53 | | |
54 | | inline uint32_t GetSegmentSize() |
55 | 0 | { |
56 | 0 | return mSegmentSize; |
57 | 0 | } |
58 | | inline uint32_t GetMaxSize() |
59 | 0 | { |
60 | 0 | return mMaxSize; |
61 | 0 | } |
62 | | inline uint32_t GetSize() |
63 | 0 | { |
64 | 0 | return GetSegmentCount() * mSegmentSize; |
65 | 0 | } |
66 | | |
67 | | inline char* GetSegment(uint32_t aIndex) |
68 | 0 | { |
69 | 0 | NS_ASSERTION(aIndex < GetSegmentCount(), "index out of bounds"); |
70 | 0 | int32_t i = ModSegArraySize(mFirstSegmentIndex + (int32_t)aIndex); |
71 | 0 | return mSegmentArray[i]; |
72 | 0 | } |
73 | | |
74 | | protected: |
75 | | inline int32_t ModSegArraySize(int32_t aIndex) |
76 | 0 | { |
77 | 0 | uint32_t result = aIndex & (mSegmentArrayCount - 1); |
78 | 0 | NS_ASSERTION(result == aIndex % mSegmentArrayCount, |
79 | 0 | "non-power-of-2 mSegmentArrayCount"); |
80 | 0 | return result; |
81 | 0 | } |
82 | | |
83 | | inline bool IsFull() |
84 | 0 | { |
85 | 0 | return ModSegArraySize(mLastSegmentIndex + 1) == mFirstSegmentIndex; |
86 | 0 | } |
87 | | |
88 | | protected: |
89 | | uint32_t mSegmentSize; |
90 | | uint32_t mMaxSize; |
91 | | char** mSegmentArray; |
92 | | uint32_t mSegmentArrayCount; |
93 | | int32_t mFirstSegmentIndex; |
94 | | int32_t mLastSegmentIndex; |
95 | | }; |
96 | | |
97 | | // NS_SEGMENTARRAY_INITIAL_SIZE: This number needs to start out as a |
98 | | // power of 2 given how it gets used. We double the segment array |
99 | | // when we overflow it, and use that fact that it's a power of 2 |
100 | | // to compute a fast modulus operation in IsFull. |
101 | | // |
102 | | // 32 segment array entries can accommodate 128k of data if segments |
103 | | // are 4k in size. That seems like a reasonable amount that will avoid |
104 | | // needing to grow the segment array. |
105 | 0 | #define NS_SEGMENTARRAY_INITIAL_COUNT 32 |
106 | | |
107 | | #endif // nsSegmentedBuffer_h__ |