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 relative relocations.
6//
7// Run-length encoded 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 <vector>
18
19#include "elf_traits.h"
20
21namespace relocation_packer {
22
23// Encode packed words as a LEB128 byte stream.
24class Leb128Encoder {
25 public:
26  // Explicit (but empty) constructor and destructor, for chromium-style.
27  Leb128Encoder();
28  ~Leb128Encoder();
29
30  // Add a value to the encoding stream.
31  // |value| is the unsigned int to add.
32  void Enqueue(ELF::Xword value);
33
34  // Add a vector of values to the encoding stream.
35  // |values| is the vector of unsigned ints to add.
36  void EnqueueAll(const std::vector<ELF::Xword>& values);
37
38  // Retrieve the encoded representation of the values.
39  // |encoding| is the returned vector of encoded data.
40  void GetEncoding(std::vector<uint8_t>* encoding) { *encoding = encoding_; }
41
42 private:
43  // Growable vector holding the encoded LEB128 stream.
44  std::vector<uint8_t> encoding_;
45};
46
47// Decode a LEB128 byte stream to produce packed words.
48class Leb128Decoder {
49 public:
50  // Create a new decoder for the given encoded stream.
51  // |encoding| is the vector of encoded data.
52  explicit Leb128Decoder(const std::vector<uint8_t>& encoding);
53
54  // Explicit (but empty) destructor, for chromium-style.
55  ~Leb128Decoder();
56
57  // Retrieve the next value from the encoded stream.
58  ELF::Xword Dequeue();
59
60  // Retrieve all remaining values from the encoded stream.
61  // |values| is the vector of decoded data.
62  void DequeueAll(std::vector<ELF::Xword>* values);
63
64 private:
65  // Encoded LEB128 stream.
66  std::vector<uint8_t> encoding_;
67
68  // Cursor indicating the current stream retrieval point.
69  size_t cursor_;
70};
71
72}  // namespace relocation_packer
73
74#endif  // TOOLS_RELOCATION_PACKER_SRC_LEB128_H_
75