local_date_time noticeably faster than ptime

[oneill1979]

We noticed recently that using a local_date_time in tight loops was several times faster than using a ptime object. As these are both based largerly on the same template code this was a surprise. It appears this is caused by the implementation of the operater+=/-= and was wondering if there was any justification for the difference or if this was just an oversight.

    //.\boost\date_time\local_time\local_date_time.hpp
    local_date_time_base operator+=(const time_duration_type& td)
    {
      this->time_ = time_system_type::add_time_duration(this->time_,td);
      return *this;
    }

    //.\boost\date_time\time.hpp
    time_type operator+=(const time_duration_type& td)
    {
      time_ = (time_system::get_time_rep(date(), time_of_day() + td));
      return time_type(time_);
    }

It looks like the ptime implementation is doing extra work to split the ptime into date and time_duration components and if it is changed to follow a similar pattern to that used in the local time the performance is then indistinguishable.

    //.\boost\date_time\time.hpp
    time_type operator+=(const time_duration_type& td)
    {
      this->time_ = time_system::add_time_duration(this->time_, td);
      return time_type(time_);
    }

I can only think that maybe this was done to work around an issue and in which case should the same then be applied to the local time implementation?

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