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 // TODO(simonb): Extend for 64-bit target libraries. 6 7 #include "leb128.h" 8 9 #include <stdint.h> 10 #include <vector> 11 12 namespace relocation_packer { 13 14 // Add a single value to the encoding. Values are encoded with variable 15 // length. The least significant 7 bits of each byte hold 7 bits of data, 16 // and the most significant bit is set on each byte except the last. Enqueue(uint32_t value)17void Leb128Encoder::Enqueue(uint32_t value) { 18 while (value > 127) { 19 encoding_.push_back((1 << 7) | (value & 127)); 20 value >>= 7; 21 } 22 encoding_.push_back(value); 23 } 24 25 // Add a vector of values to the encoding. EnqueueAll(const std::vector<uint32_t> & values)26void Leb128Encoder::EnqueueAll(const std::vector<uint32_t>& values) { 27 for (size_t i = 0; i < values.size(); ++i) 28 Enqueue(values[i]); 29 } 30 31 // Decode and retrieve a single value from the encoding. Read forwards until 32 // a byte without its most significant bit is found, then read the 7 bit 33 // fields of the bytes spanned to re-form the value. Dequeue()34uint32_t Leb128Decoder::Dequeue() { 35 size_t extent = cursor_; 36 while (encoding_[extent] >> 7) 37 extent++; 38 39 uint32_t value = 0; 40 for (size_t i = extent; i > cursor_; --i) { 41 value = (value << 7) | (encoding_[i] & 127); 42 } 43 value = (value << 7) | (encoding_[cursor_] & 127); 44 45 cursor_ = extent + 1; 46 return value; 47 } 48 49 // Decode and retrieve all remaining values from the encoding. DequeueAll(std::vector<uint32_t> * values)50void Leb128Decoder::DequeueAll(std::vector<uint32_t>* values) { 51 while (cursor_ < encoding_.size()) 52 values->push_back(Dequeue()); 53 } 54 55 } // namespace relocation_packer 56