1 // Copyright 2014 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // SLEB128 encoder and decoder for packed relative relocations. 6 // 7 // Packed relocations consist of a large number of relatively small 8 // integer values. Encoding these as LEB128 saves space. 9 // 10 // For more on LEB128 see http://en.wikipedia.org/wiki/LEB128. 11 12 #ifndef TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_ 13 #define TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_ 14 15 #include <stdint.h> 16 #include <unistd.h> 17 #include <vector> 18 19 #include "elf_traits.h" 20 21 namespace relocation_packer { 22 23 // Encode packed words as a signed LEB128 byte stream. 24 template<typename int_t> 25 class Sleb128Encoder { 26 public: 27 // Explicit (but empty) constructor and destructor, for chromium-style. 28 Sleb128Encoder(); 29 ~Sleb128Encoder(); 30 31 // Add a value to the encoding stream. 32 // |value| is the signed int to add. 33 void Enqueue(int_t value); 34 35 // Add a vector of values to the encoding stream. 36 // |values| is the vector of signed ints to add. 37 void EnqueueAll(const std::vector<int_t>& values); 38 39 // Retrieve the encoded representation of the values. 40 // |encoding| is the returned vector of encoded data. GetEncoding(std::vector<uint8_t> * encoding)41 void GetEncoding(std::vector<uint8_t>* encoding) { *encoding = encoding_; } 42 43 private: 44 // Growable vector holding the encoded LEB128 stream. 45 std::vector<uint8_t> encoding_; 46 }; 47 48 // Decode a LEB128 byte stream to produce packed words. 49 template <typename int_t> 50 class Sleb128Decoder { 51 public: 52 // Create a new decoder for the given encoded stream. 53 // |encoding| is the vector of encoded data. 54 explicit Sleb128Decoder(const std::vector<uint8_t>& encoding, size_t start_with); 55 56 // Explicit (but empty) destructor, for chromium-style. 57 ~Sleb128Decoder(); 58 59 // Retrieve the next value from the encoded stream. 60 int_t Dequeue(); 61 62 // Retrieve all remaining values from the encoded stream. 63 // |values| is the vector of decoded data. 64 void DequeueAll(std::vector<int_t>* values); 65 66 private: 67 // Encoded LEB128 stream. 68 std::vector<uint8_t> encoding_; 69 70 // Cursor indicating the current stream retrieval point. 71 size_t cursor_; 72 }; 73 74 } // namespace relocation_packer 75 76 #endif // TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_ 77