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