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 // Delta encoded relative relocations consist of a large number 8 // of pairs signed integer values, many with small values. Encoding these 9 // as signed LEB128 saves space. 10 // 11 // For more on LEB128 see http://en.wikipedia.org/wiki/LEB128. 12 13 #ifndef TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_ 14 #define TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_ 15 16 #include <stdint.h> 17 #include <unistd.h> 18 #include <vector> 19 20 #include "elf_traits.h" 21 22 namespace relocation_packer { 23 24 // Encode packed words as a signed LEB128 byte stream. 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(ELF::Sxword 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<ELF::Sxword>& values); 38 39 // Retrieve the encoded representation of the values. 40 // |encoding| is the returned vector of encoded data. 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 class Sleb128Decoder { 50 public: 51 // Create a new decoder for the given encoded stream. 52 // |encoding| is the vector of encoded data. 53 explicit Sleb128Decoder(const std::vector<uint8_t>& encoding); 54 55 // Explicit (but empty) destructor, for chromium-style. 56 ~Sleb128Decoder(); 57 58 // Retrieve the next value from the encoded stream. 59 ELF::Sxword Dequeue(); 60 61 // Retrieve all remaining values from the encoded stream. 62 // |values| is the vector of decoded data. 63 void DequeueAll(std::vector<ELF::Sxword>* values); 64 65 private: 66 // Encoded LEB128 stream. 67 std::vector<uint8_t> encoding_; 68 69 // Cursor indicating the current stream retrieval point. 70 size_t cursor_; 71 }; 72 73 } // namespace relocation_packer 74 75 #endif // TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_ 76
