sleb128.h revision 5f1c94371a64b3196d4be9466099bb892df9b88e 
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// Delta encoded relative relocations consist of a large number
8// of pairs signed integer values, many with small values.  Encoding these
9// as signed LEB128 saves space.
10//
11// For more on LEB128 see http://en.wikipedia.org/wiki/LEB128.
12
13#ifndef TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_
14#define TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_
15
16#include <stdint.h>
17#include <unistd.h>
18#include <vector>
19
20#include "elf_traits.h"
21
22namespace relocation_packer {
23
24// Encode packed words as a signed LEB128 byte stream.
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(ELF::Sxword 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<ELF::Sxword>& 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.
49class Sleb128Decoder {
50 public:
51  // Create a new decoder for the given encoded stream.
52  // |encoding| is the vector of encoded data.
53  explicit Sleb128Decoder(const std::vector<uint8_t>& encoding);
54
55  // Explicit (but empty) destructor, for chromium-style.
56  ~Sleb128Decoder();
57
58  // Retrieve the next value from the encoded stream.
59  ELF::Sxword Dequeue();
60
61  // Retrieve all remaining values from the encoded stream.
62  // |values| is the vector of decoded data.
63  void DequeueAll(std::vector<ELF::Sxword>* values);
64
65 private:
66  // Encoded LEB128 stream.
67  std::vector<uint8_t> encoding_;
68
69  // Cursor indicating the current stream retrieval point.
70  size_t cursor_;
71};
72
73}  // namespace relocation_packer
74
75#endif  // TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_
76