leb128.h revision f8ee788a64d60abd8f2d742a5fdedde054ecd910 
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// LEB128 encoder and decoder for packed R_ARM_RELATIVE relocations.
6//
7// Run-length encoded R_ARM_RELATIVE relocations consist of a large number
8// of pairs of relatively small positive integer values.  Encoding these as
9// LEB128 saves space.
10//
11// For more on LEB128 see http://en.wikipedia.org/wiki/LEB128.
12
13#ifndef TOOLS_RELOCATION_PACKER_SRC_LEB128_H_
14#define TOOLS_RELOCATION_PACKER_SRC_LEB128_H_
15
16#include <stdint.h>
17#include <unistd.h>
18#include <vector>
19
20namespace relocation_packer {
21
22// Encode packed words as a LEB128 byte stream.
23class Leb128Encoder {
24 public:
25  // Add a value to the encoding stream.
26  // |value| is the unsigned int to add.
27  void Enqueue(uint32_t value);
28
29  // Add a vector of values to the encoding stream.
30  // |values| is the vector of unsigned ints to add.
31  void EnqueueAll(const std::vector<uint32_t>& values);
32
33  // Retrieve the encoded representation of the values.
34  // |encoding| is the returned vector of encoded data.
35  void GetEncoding(std::vector<uint8_t>* encoding) { *encoding = encoding_; }
36
37 private:
38  // Growable vector holding the encoded LEB128 stream.
39  std::vector<uint8_t> encoding_;
40};
41
42// Decode a LEB128 byte stream to produce packed words.
43class Leb128Decoder {
44 public:
45  // Create a new decoder for the given encoded stream.
46  // |encoding| is the vector of encoded data.
47  explicit Leb128Decoder(const std::vector<uint8_t>& encoding)
48      : encoding_(encoding), cursor_(0) { }
49
50  // Retrieve the next value from the encoded stream.
51  uint32_t Dequeue();
52
53  // Retrieve all remaining values from the encoded stream.
54  // |values| is the vector of decoded data.
55  void DequeueAll(std::vector<uint32_t>* values);
56
57 private:
58  // Encoded LEB128 stream.
59  std::vector<uint8_t> encoding_;
60
61  // Cursor indicating the current stream retrieval point.
62  size_t cursor_;
63};
64
65}  // namespace relocation_packer
66
67#endif  // TOOLS_RELOCATION_PACKER_SRC_LEB128_H_
68