text: #ifndef BOOST_SMART_PTR_DETAIL_SP_COUNTED_BASE_SYNC_HPP_INCLUDED
  #define BOOST_SMART_PTR_DETAIL_SP_COUNTED_BASE_SYNC_HPP_INCLUDED
  
  // MS compatible compilers support #pragma once
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1020)
  # pragma once
  #endif
  
  //  detail/sp_counted_base_sync.hpp - g++ 4.1+ __sync intrinsics
  //
  //  Copyright (c) 2007 Peter Dimov
  //
  //  Distributed under the Boost Software License, Version 1.0.
  //  See accompanying file LICENSE_1_0.txt or copy at
  //  http://www.boost.org/LICENSE_1_0.txt
  
  #include <boost/detail/sp_typeinfo.hpp>
  #include <limits.h>
  
  #if defined( __ia64__ ) && defined( __INTEL_COMPILER )
  # include <ia64intrin.h>
  #endif
  
  namespace boost
  {
  
  namespace detail
  {
  
  #if INT_MAX >= 2147483647
  
  typedef int sp_int32_t;
  
  #else
  
  typedef long sp_int32_t;
  
  #endif
  
  inline void atomic_increment( sp_int32_t * pw )
  {
      __sync_fetch_and_add( pw, 1 );
  }
  
  inline sp_int32_t atomic_decrement( sp_int32_t * pw )
  {
      return __sync_fetch_and_add( pw, -1 );
  }
  
  inline sp_int32_t atomic_conditional_increment( sp_int32_t * pw )
  {
      // long r = *pw;
      // if( r != 0 ) ++*pw;
      // return r;
  
      sp_int32_t r = *pw;
  
      for( ;; )
      {
          if( r == 0 )
          {
              return r;
          }
  
          sp_int32_t r2 = __sync_val_compare_and_swap( pw, r, r + 1 );
  
          if( r2 == r )
          {
              return r;
          }
          else
          {
              r = r2;
          }
      }    
  }
  
  class sp_counted_base
  {
  private:
  
      sp_counted_base( sp_counted_base const & );
      sp_counted_base & operator= ( sp_counted_base const & );
  
      sp_int32_t use_count_;        // #shared
      sp_int32_t weak_count_;       // #weak + (#shared != 0)
  
  public:
  
      sp_counted_base(): use_count_( 1 ), weak_count_( 1 )
      {
      }
  
      virtual ~sp_counted_base() // nothrow
      {
      }
  
      // dispose() is called when use_count_ drops to zero, to release
      // the resources managed by *this.
  
      virtual void dispose() = 0; // nothrow
  
      // destroy() is called when weak_count_ drops to zero.
  
      virtual void destroy() // nothrow
      {
          delete this;
      }
  
      virtual void * get_deleter( sp_typeinfo const & ti ) = 0;
      virtual void * get_untyped_deleter() = 0;
  
      void add_ref_copy()
      {
          atomic_increment( &use_count_ );
      }
  
      bool add_ref_lock() // true on success
      {
          return atomic_conditional_increment( &use_count_ ) != 0;
      }
  
      void release() // nothrow
      {
          if( atomic_decrement( &use_count_ ) == 1 )
          {
              dispose();
              weak_release();
          }
      }
  
      void weak_add_ref() // nothrow
      {
          atomic_increment( &weak_count_ );
      }
  
      void weak_release() // nothrow
      {
          if( atomic_decrement( &weak_count_ ) == 1 )
          {
              destroy();
          }
      }
  
      long use_count() const // nothrow
      {
          return const_cast< sp_int32_t const volatile & >( use_count_ );
      }
  };
  
  } // namespace detail
  
  } // namespace boost
  
  #endif  // #ifndef BOOST_SMART_PTR_DETAIL_SP_COUNTED_BASE_SYNC_HPP_INCLUDED
  