DVLCast.h

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// This file's extension implies that it's C, but it's really -*- C++ -*-.
 
/*
  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
*/
 
// $Id$
 
 
#ifndef ATHCONTAINERS_TOOLS_DVLCAST_H
#define ATHCONTAINERS_TOOLS_DVLCAST_H
 
 
#include <limits>
#include <limits.h>
#include <typeinfo>
#include <cstdlib>
#include <cstddef>
 
 
namespace DataModel_detail {
 

template <class DVL, bool has_virtual=DVL::has_virtual> struct DVLCast {};
 

template <class DVL>
struct DVLCast<DVL, false>
{
  typedef typename DVL::base_value_type T;
 

  template <class U>
  static T* cast (U* b)
  {
    return static_cast<T*> (b);
  }
 

  template <class U>
  static const T* cast (const U* b)
  {
    return static_cast<const T*> (b);
  }
};
 

template <class DVL>
struct DVLCast<DVL, true>
{
  typedef typename DVL::base_value_type T;
 

  template <class U>
  static int find_offset (U* b)
  {
    T* ret = dynamic_cast<T*> (b);
    int offs = reinterpret_cast<char*>(ret) - reinterpret_cast<char*>(b);
    return offs;
  }
 

  template <class U>
  static T* cast (U* b)
  {
    // The common case will be for the dynamic type of b to be T.
    // So test to avoid a dynamic_cast in that case.
    // The extra test shouldn't add significant overhead
    // to the case where we really need to run dynamic_cast.
    if (!b)
      return 0;
    if (typeid(*b) == typeid(T)) {
      static const ptrdiff_t offs = find_offset (b);
      return reinterpret_cast<T*> (reinterpret_cast<char*>(b) + offs);
    }
    else
      return dynamic_cast<T*> (b);
  }
 

  template <class U>
  static const T* cast (const U* b)
  {
    // See above.
    if (!b)
      return 0;
    if (typeid(*b) == typeid(T)) {
      static ptrdiff_t offs = LONG_MAX;
      if (offs == LONG_MAX) {
        T* ret = dynamic_cast<const T*> (b);
        offs = reinterpret_cast<char*>(ret) - reinterpret_cast<char*>(b);
        return ret;
      }
      return reinterpret_cast<const T*> (reinterpret_cast<char*>(b) + offs);
    }
    else
      return dynamic_cast<const T*> (b);
  }
};
 
 
} // namespace DataModel_detail
 
 
#endif // not ATHCONTAINERS_TOOLS_DVLCAST_H