[Boost-bugs] [Boost C++ Libraries] #2718: local_date_time noticeably faster than ptime

Subject: [Boost-bugs] [Boost C++ Libraries] #2718: local_date_time noticeably faster than ptime
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-02-03 09:14:19

#2718: local_date_time noticeably faster than ptime
------------------------------+---------------------------------------------
 Reporter:  oneill1979        |       Owner:  az_sw_dude  
     Type:  Bugs              |      Status:  new         
Milestone:  To Be Determined  |   Component:  date_time   
  Version:  Boost 1.37.0      |    Severity:  Optimization
 Keywords:                    |  
------------------------------+---------------------------------------------
 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.

 {{{
 #!cpp
     //.\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;
     }
 }}}

 {{{
 #!cpp
     //.\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.

 {{{
 #!cpp
     //.\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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Ticket URL: <https://svn.boost.org/trac/boost/ticket/2718>
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