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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_LIBDEXFILE_DEX_COMPACT_OFFSET_TABLE_H_
#define ART_LIBDEXFILE_DEX_COMPACT_OFFSET_TABLE_H_
#include <cstdint>
#include <vector>
namespace art {
// Compact offset table that aims to minimize size while still providing reasonable speed (10-20ns
// average time per lookup on host).
class CompactOffsetTable {
public:
// This value is coupled with the leb chunk bitmask. That logic must also be adjusted when the
// integer is modified.
static constexpr std::size_t kElementsPerIndex = 16;
// Leb block format:
// [uint16_t] 16 bit mask for what indexes actually have a non zero offset for the chunk.
// [lebs] Up to 16 lebs encoded using leb128, one leb bit. The leb specifies how the offset
// changes compared to the previous index.
class Accessor {
public:
// Read the minimum and table offsets from the data pointer.
explicit Accessor(const uint8_t* data_begin);
Accessor(const uint8_t* data_begin, uint32_t minimum_offset, uint32_t table_offset);
// Return the offset for the index.
uint32_t GetOffset(uint32_t index) const;
private:
const uint32_t* const table_;
const uint32_t minimum_offset_;
const uint8_t* const data_begin_;
};
// Version that also serializes the min offset and table offset.
static void Build(const std::vector<uint32_t>& offsets, std::vector<uint8_t>* out_data);
// Returned offsets are all relative to out_min_offset.
static void Build(const std::vector<uint32_t>& offsets,
std::vector<uint8_t>* out_data,
uint32_t* out_min_offset,
uint32_t* out_table_offset);
// 32 bit aligned for the offset table.
static constexpr std::size_t kAlignment = sizeof(uint32_t);
};
} // namespace art
#endif // ART_LIBDEXFILE_DEX_COMPACT_OFFSET_TABLE_H_
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