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 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(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.
  49 class 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_