third_party/android_platform/bionic/tools/relocation_packer/src/sleb128.h

   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
  22 namespace relocation_packer {
  23
  24 // Encode packed words as a signed LEB128 byte stream.
  25 template<typename int_t>
  26 class Sleb128Encoder {
  27  public:
  28   // Explicit (but empty) constructor and destructor, for chromium-style.
  29   Sleb128Encoder();
  30   ~Sleb128Encoder();
  31
  32   // Add a value to the encoding stream.
  33   // |value| is the signed int to add.
  34   void Enqueue(int_t value);
  35
  36   // Add a vector of values to the encoding stream.
  37   // |values| is the vector of signed ints to add.
  38   void EnqueueAll(const std::vector<int_t>& values);
  39
  40   // Retrieve the encoded representation of the values.
  41   // |encoding| is the returned vector of encoded data.
  42   void GetEncoding(std::vector<uint8_t>* encoding) { *encoding = encoding_; }
  43
  44  private:
  45   // Growable vector holding the encoded LEB128 stream.
  46   std::vector<uint8_t> encoding_;
  47 };
  48
  49 // Decode a LEB128 byte stream to produce packed words.
  50 template <typename int_t>
  51 class Sleb128Decoder {
  52  public:
  53   // Create a new decoder for the given encoded stream.
  54   // |encoding| is the vector of encoded data.
  55   explicit Sleb128Decoder(const std::vector<uint8_t>& encoding, size_t start_with);
  56
  57   // Explicit (but empty) destructor, for chromium-style.
  58   ~Sleb128Decoder();
  59
  60   // Retrieve the next value from the encoded stream.
  61   int_t Dequeue();
  62
  63   // Retrieve all remaining values from the encoded stream.
  64   // |values| is the vector of decoded data.
  65   void DequeueAll(std::vector<int_t>* values);
  66
  67  private:
  68   // Encoded LEB128 stream.
  69   std::vector<uint8_t> encoding_;
  70
  71   // Cursor indicating the current stream retrieval point.
  72   size_t cursor_;
  73 };
  74
  75 }  // namespace relocation_packer
  76
  77 #endif  // TOOLS_RELOCATION_PACKER_SRC_SLEB128_H_