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 #include "leb128.h" 6 7 #include <stdint.h> 8 #include <vector> 9 10 #include "elf_traits.h" 11 12 namespace relocation_packer { 13 14 // Empty constructor and destructor to silence chromium-style. 15 Leb128Encoder::Leb128Encoder() { } 16 Leb128Encoder::~Leb128Encoder() { } 17 18 // Add a single value to the encoding. Values are encoded with variable 19 // length. The least significant 7 bits of each byte hold 7 bits of data, 20 // and the most significant bit is set on each byte except the last. 21 void Leb128Encoder::Enqueue(ELF::Xword value) { 22 do { 23 const uint8_t byte = value & 127; 24 value >>= 7; 25 encoding_.push_back((value ? 128 : 0) | byte); 26 } while (value); 27 } 28 29 // Add a vector of values to the encoding. 30 void Leb128Encoder::EnqueueAll(const std::vector<ELF::Xword>& values) { 31 for (size_t i = 0; i < values.size(); ++i) 32 Enqueue(values[i]); 33 } 34 35 // Create a new decoder for the given encoded stream. 36 Leb128Decoder::Leb128Decoder(const std::vector<uint8_t>& encoding) { 37 encoding_ = encoding; 38 cursor_ = 0; 39 } 40 41 // Empty destructor to silence chromium-style. 42 Leb128Decoder::~Leb128Decoder() { } 43 44 // Decode and retrieve a single value from the encoding. Read forwards until 45 // a byte without its most significant bit is found, then read the 7 bit 46 // fields of the bytes spanned to re-form the value. 47 ELF::Xword Leb128Decoder::Dequeue() { 48 ELF::Xword value = 0; 49 50 size_t shift = 0; 51 uint8_t byte; 52 53 // Loop until we reach a byte with its high order bit clear. 54 do { 55 byte = encoding_[cursor_++]; 56 value |= static_cast<ELF::Xword>(byte & 127) << shift; 57 shift += 7; 58 } while (byte & 128); 59 60 return value; 61 } 62 63 // Decode and retrieve all remaining values from the encoding. 64 void Leb128Decoder::DequeueAll(std::vector<ELF::Xword>* values) { 65 while (cursor_ < encoding_.size()) 66 values->push_back(Dequeue()); 67 } 68 69 } // namespace relocation_packer 70
