tools/relocation_packer/src/leb128.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 // 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
  21 namespace relocation_packer {
  22
  23 // Encode packed words as a LEB128 byte stream.
  24 class 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.
  48 class 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_