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 
21 namespace relocation_packer {
22 
23 // Encode packed words as a signed LEB128 byte stream.
24 template<typename int_t>
25 class 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.
GetEncoding(std::vector<uint8_t> * encoding)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.
49 template <typename int_t>
50 class 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