segment.h

Linux下一个可以比较二进制文件的工具xdelta3.0u的源码。

// -*- Mode: C++ -*-

namespace regtest {

class Segment {
 public:
  Segment(size_t size, MTRandom *rand)
    : size_(size),
      seed_(rand->Rand32()),
      seed_offset_(0),
      data_(NULL) { 
    CHECK_GT(size_, 0);
  }

  Segment(size_t size, uint32_t seed)
    : size_(size),
      seed_(seed),
      seed_offset_(0),
      data_(NULL) { 
    CHECK_GT(size_, 0);
  }

  Segment(size_t size, uint8_t *data)
    : size_(size),
      seed_(0),
      seed_offset_(0),
      data_(data) { 
    CHECK_GT(size_, 0);
  }

  size_t Size() const {
    return size_; 
  }

  Segment Subseg(size_t start, size_t size) const {
    CHECK_LE(start + size, size_);
    if (data_) {
      return Segment(size, data_ + start);
    } else {
      return Segment(size, seed_, seed_offset_ + start);
    }
  }

  void Fill(size_t seg_offset, size_t size, uint8_t *data) const {
    CHECK_LE(seg_offset + size, size_);
    if (data_) {
      memcpy(data, data_ + seg_offset, size);
    } else {
      size_t skip = seg_offset + seed_offset_;
      MTRandom gen(seed_);
      MTRandom8 gen8(&gen);
      while (skip--) {
	gen8.Rand8();
      }
      for (size_t i = 0; i < size; i++) {
	data[i] = gen8.Rand8();
      }
    }
  }

private:
  // Used by Subseg()
  Segment(size_t size, uint32_t seed, size_t seed_offset)
    : size_(size),
      seed_(seed),
      seed_offset_(seed_offset),
      data_(NULL) {
    CHECK_GT(size_, 0);
  }

  friend ostream& operator<<(ostream& os, const Segment &seg);

  size_t size_;  // Size of this segment

  // For random segments
  uint32_t seed_;  // Seed used for generating byte sequence
  size_t seed_offset_;  // Seed positions the sequence this many bytes
                        // before its beginning.

  // For literal segments (data is not owned)
  uint8_t *data_;
};

ostream& operator<<(ostream& os, const Segment &seg) {
  if (seg.data_) {
    for (size_t i = 0; i < seg.size_; i++) {
      char buf[10];
      sprintf(buf, "%02x ", seg.data_[i]);
      os << buf;
    }
    return os;
  } else {
    return os << "size=" << seg.size_ << ",seed=" << seg.seed_
	      << ",skip=" << seg.seed_offset_;
  }
}

typedef map<xoff_t, Segment> SegmentMap;

}  // namespace regtest