[Boost-bugs] [Boost C++ Libraries] #3471: microseconds constructor overflows

Subject: [Boost-bugs] [Boost C++ Libraries] #3471: microseconds constructor overflows
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-09-21 16:19:26

#3471: microseconds constructor overflows
--------------------------+-------------------------------------------------
 Reporter:  andysem       |       Owner:  az_sw_dude
     Type:  Bugs          |      Status:  new       
Milestone:  Boost 1.41.0  |   Component:  date_time 
  Version:  Boost 1.40.0  |    Severity:  Problem   
 Keywords:  microseconds  |  
--------------------------+-------------------------------------------------
 From the users ML: [http://lists.boost.org/boost-users/2008/10/41763.php]

 The boost::date_time::microseconds(...) constructor overflows the int64
 size
 limits in intermediary calculations. The code below will reproduce the
 error
 (using VC++ 2008 and boost 1.36).

 {{{
 ptime start(boost::gregorian::date(2000, 1, 1));
 ptime end(boost::gregorian::date(2000, 5, 1));
 time_duration td = end - start;

 ptime wrongEnd = start + microseconds(td.total_microseconds());
 BOOST_CHECK_EQUAL(end, wrongEnd);
 }}}

 The microseconds constructor takes an int64 as input and the
 total_microseconds is well within its range. Inside the
 date_time::subsecond_duration<time_duration, 1000000> the internal
 duration
 is calculated as

 {{{
 ss*traits_type::res_adjust()/frac_of_second
 }}}

 Since the both res_adjust() and frac_of_second have the value 1000000, the
 result should be ss*1 but... the intermediary value ss*res_adjust
 overflows
 the int64 causing a negative number to be returned.

 Question is, is this by design or is it a bug? I'm rather new to
 boost::date_time and was hoping to replace our current datetime types with
 it. We are using millisecond timestamped data over long time series
 (years).

 I guess the simple solution would be to add parentheses around
 (res_adjust()/frac_of_second) assuming frac_of_second always divides
 res_adjust. However, there are similar issues when adding 200 years worth
 of
 seconds which overflows the int32 argument (but that's not of my immediate
 concern).

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3471>
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