boost/smart_ptr/detail/atomic_count_gcc_x86.hpp

#ifndef BOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_GCC_X86_HPP_INCLUDED
#define BOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_GCC_X86_HPP_INCLUDED
//
//  boost/detail/atomic_count_gcc_x86.hpp
//
//  atomic_count for g++ on 486+/AMD64
//
//  Copyright 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)
//
namespace boost
{
namespace detail
{
class atomic_count
{
public:
    explicit atomic_count( long v ) : value_( static_cast< int >( v ) ) {}
    long operator++()
    {
        return atomic_exchange_and_add( &value_, +1 ) + 1;
    }
    long operator--()
    {
        return atomic_exchange_and_add( &value_, -1 ) - 1;
    }
    operator long() const
    {
        return atomic_exchange_and_add( &value_, 0 );
    }
private:
    atomic_count(atomic_count const &);
    atomic_count & operator=(atomic_count const &);
    mutable int value_;
private:
    static int atomic_exchange_and_add( int * pw, int dv )
    {
        // int r = *pw;
        // *pw += dv;
        // return r;
        int r;
        __asm__ __volatile__
        (
            "lock\n\t"
            "xadd %1, %0":
            "+m"( *pw ), "=r"( r ): // outputs (%0, %1)
            "1"( dv ): // inputs (%2 == %1)
            "memory", "cc" // clobbers
        );
        return r;
    }
};
} // namespace detail
} // namespace boost
#endif // #ifndef BOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_GCC_X86_HPP_INCLUDED