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// Packed relocations consist of a large number of relatively small
8// integer values.  Encoding these as LEB128 saves space.
9//
10// For more on LEB128 see http://en.wikipedia.org/wiki/LEB128.
11
12#ifndef TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_
13#define TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_
14
15#include <stdint.h>
16#include <unistd.h>
17#include <vector>
18
19#include "elf_traits.h"
20
21namespace relocation_packer {
22
23// Encode packed words as a signed LEB128 byte stream.
24template<typename int_t>
25class 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(int_t 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<int_t>& 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.
49template <typename int_t>
50class Sleb128Decoder {
51 public:
52  // Create a new decoder for the given encoded stream.
53  // |encoding| is the vector of encoded data.
54  explicit Sleb128Decoder(const std::vector<uint8_t>& encoding, size_t start_with);
55
56  // Explicit (but empty) destructor, for chromium-style.
57  ~Sleb128Decoder();
58
59  // Retrieve the next value from the encoded stream.
60  int_t Dequeue();
61
62  // Retrieve all remaining values from the encoded stream.
63  // |values| is the vector of decoded data.
64  void DequeueAll(std::vector<int_t>* values);
65
66 private:
67  // Encoded LEB128 stream.
68  std::vector<uint8_t> encoding_;
69
70  // Cursor indicating the current stream retrieval point.
71  size_t cursor_;
72};
73
74}  // namespace relocation_packer
75
76#endif  // TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_
77