mayown_ptr.h

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#ifndef CMSSW_mayown_ptr_H
#define CMSSW_mayown_ptr_H

#include <cassert>
#include <cstring>

// a smart pointer which may own
// can be implemented trivially with shared_ptr
// this is infinetely ligher
// assume alignment > 2....

template <typename T, int N = sizeof(T*)>
class mayown_ptr {
private:
  T const* p = nullptr;

  void markOwn() {
    if (nullptr == p)
      return;
    unsigned char buff[N];
    memcpy(buff, &p, N);
    assert((buff[N - 1] & 1) == 0);
    ++buff[N - 1];
    memcpy(&p, buff, N);
  }

public:
  bool isOwn() const {
    unsigned char buff[N];
    memcpy(buff, &p, N);
    return 1 == (buff[N - 1] & 1);
  }

private:
  T const* pointer() const {
    unsigned char buff[N];
    memcpy(buff, &p, N);
    buff[N - 1] &= 0xFE;
    assert((buff[N - 1] & 1) == 0);
    T const* np;
    memcpy(&np, buff, N);
    return np;
  }

  void destroy() {
    if (isOwn())
      delete const_cast<T*>(pointer());
  }

public:
  explicit mayown_ptr(T* ip = nullptr) : p(ip) { markOwn(); }
  explicit mayown_ptr(T const& ip) : p(&ip) {}
  ~mayown_ptr() { destroy(); }
  mayown_ptr(mayown_ptr&) = delete;
  mayown_ptr(mayown_ptr&& rh) : p(rh.p) { rh.p = nullptr; }
  mayown_ptr& operator=(mayown_ptr&) = delete;
  mayown_ptr& operator=(mayown_ptr&& rh) {
    destroy();
    p = rh.p;
    rh.p = nullptr;
    return *this;
  }

  T const& operator*() const { return *pointer(); }
  T const* operator->() const { return pointer(); }
  T const* get() const { return pointer(); }
  T const* release() {
    auto np = pointer();
    p = nullptr;
    return np;
  }
  void reset() {
    destroy();
    p = nullptr;
  }
  void reset(T* ip) {
    destroy();
    p = ip;
    markOwn();
  }
  void reset(T const& ip) {
    destroy();
    p = &ip;
  }
  bool empty() const { return nullptr == p; }

  T const* raw() const { return p; }
};

template <typename T>
bool operator==(mayown_ptr<T> const& rh, mayown_ptr<T> const& lh) {
  return rh.raw() == lh.raw();
}
template <typename T>
bool operator<(mayown_ptr<T> const& rh, mayown_ptr<T> const& lh) {
  return rh.raw() < lh.raw();
}

#endif