Boost и побайтное чтение/запись в файл

void _copy_file(const char *FromFile, const char *ToFile, int bufsize)
{
    ifstream stream;
    long long tmp = 0;
    long long fSize = 0;
    char* buffer = new char[bufsize];
 
    stream.open(FromFile, BOOST_IOS::binary);
    file_sink out(ToFile, BOOST_IOS::binary);
    stream.seekg(0, BOOST_IOS::end);
    fSize = stream.tellg();
    stream.seekg(0, BOOST_IOS::beg);    
 
    if (fSize < bufsize) 
    {
        stream.read(buffer, fSize);
        out.write(buffer, fSize);
        return;
    }   
 
    while(stream)
    {
        if ((fSize - tmp) < bufsize)
        {
          stream.read(buffer, (fSize - tmp));
          out.write(buffer, (fSize - tmp));
          break;
        }
        stream.read(buffer, bufsize);
        out.write(buffer, bufsize);
        tmp += bufsize;     
    }
}
 
void boost_copy_file(const char *FromFile, const char *ToFile, int bufsize)
{
    size_t num_threads = boost::thread::hardware_concurrency();
    boost::thread_group threads;
 
    for (int i = 0; i < num_threads; ++i)
        threads.create_thread(boost::bind(&_copy_file, FromFile, ToFile, bufsize));
    threads.join_all(); 
}