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segment.h

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

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();
      }
    }
  }

  string ToString() const {
    string r;
    if (data_) {
      for (size_t i = 0; i < size_; i++) {
      char buf[10];
      sprintf(buf, "%02x ", data_[i]);
      r.append(buf);
      }
    } else {
      char buf[256];
      sprintf(buf, "size=%ld,seed=%ld,skip=%ld", size_, seed_, seed_offset_);
      r.append(buf);
    }
    return r;
  }

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);
  }

  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_;
};

typedef map<xoff_t, Segment> SegmentMap;
typedef typename SegmentMap::const_iterator ConstSegmentMapIterator;
typedef typename SegmentMap::iterator SegmentMapIterator;

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