// pointer to a 3D array element; this class is nested within zfp::array3
class pointer {
public:
  pointer() : ref(0, 0, 0, 0) {}
  pointer operator=(const pointer& p) { ref.array = p.ref.array; ref.i = p.ref.i; ref.j = p.ref.j; ref.k = p.ref.k; return *this; }
  reference operator*() const { return ref; }
  reference operator[](ptrdiff_t d) const { return *operator+(d); }
  pointer& operator++() { increment(); return *this; }
  pointer& operator--() { decrement(); return *this; }
  pointer operator++(int) { pointer p = *this; increment(); return p; }
  pointer operator--(int) { pointer p = *this; decrement(); return p; }
  pointer operator+=(ptrdiff_t d) { set(index() + d); return *this; }
  pointer operator-=(ptrdiff_t d) { set(index() - d); return *this; }
  pointer operator+(ptrdiff_t d) const { pointer p = *this; p += d; return p; }
  pointer operator-(ptrdiff_t d) const { pointer p = *this; p -= d; return p; }
  ptrdiff_t operator-(const pointer& p) const { return index() - p.index(); }
  bool operator==(const pointer& p) const { return ref.array == p.ref.array && ref.i == p.ref.i && ref.j == p.ref.j && ref.k == p.ref.k; }
  bool operator!=(const pointer& p) const { return !operator==(p); }

protected:
  friend class array3;
  friend class reference;
  explicit pointer(reference r) : ref(r) {}
  explicit pointer(array3* array, uint i, uint j, uint k) : ref(array, i, j, k) {}
  ptrdiff_t index() const { return ref.i + ref.array->nx * (ref.j + ref.array->ny * ref.k); }
  void set(ptrdiff_t index) { ref.array->ijk(ref.i, ref.j, ref.k, index); }
  void increment()
  {
    if (++ref.i == ref.array->nx) {
      ref.i = 0;
      if (++ref.j == ref.array->ny) {
        ref.j = 0;
        ref.k++;
      }
    }
  }
  void decrement()
  {
    if (!ref.i--) {
      ref.i = ref.array->nx - 1;
      if (!ref.j--) {
        ref.j = ref.array->ny - 1;
        ref.k--;
      }
    }
  }
  reference ref;
};