1 /*
2  * Copyright (C) 2013, The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *     http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef LATINIME_BUFFER_WITH_EXTENDABLE_BUFFER_H
18 #define LATINIME_BUFFER_WITH_EXTENDABLE_BUFFER_H
19 
20 #include <cstddef>
21 #include <cstdint>
22 #include <vector>
23 
24 #include "defines.h"
25 #include "dictionary/utils/byte_array_utils.h"
26 #include "utils/byte_array_view.h"
27 
28 namespace latinime {
29 
30 // This is used as a buffer that can be extended for updatable dictionaries.
31 // To optimize performance, raw pointer is directly used for reading buffer. The position has to be
32 // adjusted to access additional buffer. On the other hand, this class does not provide writable
33 // raw pointer but provides several methods that handle boundary checking for writing data.
34 class BufferWithExtendableBuffer {
35  public:
36     static const size_t DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE;
37 
BufferWithExtendableBuffer(const ReadWriteByteArrayView originalBuffer,const int maxAdditionalBufferSize)38     BufferWithExtendableBuffer(const ReadWriteByteArrayView originalBuffer,
39             const int maxAdditionalBufferSize)
40             : mOriginalBuffer(originalBuffer), mAdditionalBuffer(), mUsedAdditionalBufferSize(0),
41               mMaxAdditionalBufferSize(maxAdditionalBufferSize) {}
42 
43     // Without original buffer.
BufferWithExtendableBuffer(const int maxAdditionalBufferSize)44     BufferWithExtendableBuffer(const int maxAdditionalBufferSize)
45             : mOriginalBuffer(), mAdditionalBuffer(), mUsedAdditionalBufferSize(0),
46               mMaxAdditionalBufferSize(maxAdditionalBufferSize) {}
47 
getTailPosition()48     AK_FORCE_INLINE int getTailPosition() const {
49         return mOriginalBuffer.size() + mUsedAdditionalBufferSize;
50     }
51 
getUsedAdditionalBufferSize()52     AK_FORCE_INLINE int getUsedAdditionalBufferSize() const {
53         return mUsedAdditionalBufferSize;
54     }
55 
56     /**
57      * For reading.
58      */
isInAdditionalBuffer(const int position)59     AK_FORCE_INLINE bool isInAdditionalBuffer(const int position) const {
60         return position >= static_cast<int>(mOriginalBuffer.size());
61     }
62 
63     // TODO: Resolve the issue that the address can be changed when the vector is resized.
64     // CAVEAT!: Be careful about array out of bound access with buffers
getBuffer(const bool usesAdditionalBuffer)65     AK_FORCE_INLINE const uint8_t *getBuffer(const bool usesAdditionalBuffer) const {
66         if (usesAdditionalBuffer) {
67             return mAdditionalBuffer.data();
68         } else {
69             return mOriginalBuffer.data();
70         }
71     }
72 
73     uint32_t readUint(const int size, const int pos) const;
74 
75     uint32_t readUintAndAdvancePosition(const int size, int *const pos) const;
76 
77     void readCodePointsAndAdvancePosition(const int maxCodePointCount,
78             int *const outCodePoints, int *outCodePointCount, int *const pos) const;
79 
getOriginalBufferSize()80     AK_FORCE_INLINE int getOriginalBufferSize() const {
81         return mOriginalBuffer.size();
82     }
83 
isNearSizeLimit()84     AK_FORCE_INLINE bool isNearSizeLimit() const {
85         return mAdditionalBuffer.size() >= ((mMaxAdditionalBufferSize
86                 * NEAR_BUFFER_LIMIT_THRESHOLD_PERCENTILE) / 100);
87     }
88 
89     bool extend(const int size);
90 
91     /**
92      * For writing.
93      *
94      * Writing is allowed for original buffer, already written region of additional buffer and the
95      * tail of additional buffer.
96      */
97     bool writeUint(const uint32_t data, const int size, const int pos);
98 
99     bool writeUintAndAdvancePosition(const uint32_t data, const int size, int *const pos);
100 
101     bool writeCodePointsAndAdvancePosition(const int *const codePoints, const int codePointCount,
102             const bool writesTerminator, int *const pos);
103 
104     bool copy(const BufferWithExtendableBuffer *const sourceBuffer);
105 
106  private:
107     DISALLOW_COPY_AND_ASSIGN(BufferWithExtendableBuffer);
108 
109     static const int NEAR_BUFFER_LIMIT_THRESHOLD_PERCENTILE;
110     static const size_t EXTEND_ADDITIONAL_BUFFER_SIZE_STEP;
111 
112     const ReadWriteByteArrayView mOriginalBuffer;
113     std::vector<uint8_t> mAdditionalBuffer;
114     int mUsedAdditionalBufferSize;
115     const size_t mMaxAdditionalBufferSize;
116 
117     // Return if the buffer is successfully extended or not.
118     bool extendBuffer(const size_t size);
119 
120     // Returns if it is possible to write size-bytes from pos. When pos is at the tail position of
121     // the additional buffer, try extending the buffer.
122     bool checkAndPrepareWriting(const int pos, const int size);
123 };
124 }
125 #endif /* LATINIME_BUFFER_WITH_EXTENDABLE_BUFFER_H */
126