1/*
2 * Copyright (C) 2018 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 ART_LIBDEXFILE_DEX_COMPACT_OFFSET_TABLE_H_
18#define ART_LIBDEXFILE_DEX_COMPACT_OFFSET_TABLE_H_
19
20#include <cstdint>
21#include <vector>
22
23namespace art {
24
25// Compact offset table that aims to minimize size while still providing reasonable speed (10-20ns
26// average time per lookup on host).
27class CompactOffsetTable {
28 public:
29  // This value is coupled with the leb chunk bitmask. That logic must also be adjusted when the
30  // integer is modified.
31  static constexpr size_t kElementsPerIndex = 16;
32
33  // Leb block format:
34  // [uint16_t] 16 bit mask for what indexes actually have a non zero offset for the chunk.
35  // [lebs] Up to 16 lebs encoded using leb128, one leb bit. The leb specifies how the offset
36  // changes compared to the previous index.
37
38  class Accessor {
39   public:
40    // Read the minimum and table offsets from the data pointer.
41    explicit Accessor(const uint8_t* data_begin);
42
43    Accessor(const uint8_t* data_begin, uint32_t minimum_offset, uint32_t table_offset);
44
45    // Return the offset for the index.
46    uint32_t GetOffset(uint32_t index) const;
47
48   private:
49    const uint32_t* const table_;
50    const uint32_t minimum_offset_;
51    const uint8_t* const data_begin_;
52  };
53
54  // Version that also serializes the min offset and table offset.
55  static void Build(const std::vector<uint32_t>& offsets, std::vector<uint8_t>* out_data);
56
57  // Returned offsets are all relative to out_min_offset.
58  static void Build(const std::vector<uint32_t>& offsets,
59                    std::vector<uint8_t>* out_data,
60                    uint32_t* out_min_offset,
61                    uint32_t* out_table_offset);
62
63  // 32 bit aligned for the offset table.
64  static constexpr size_t kAlignment = sizeof(uint32_t);
65};
66
67}  // namespace art
68
69#endif  // ART_LIBDEXFILE_DEX_COMPACT_OFFSET_TABLE_H_
70