[boost] [date_time] int64 overflow bug with subsecond duration

Subject: [boost] [date_time] int64 overflow bug with subsecond duration
From: Zachary Turner (divisortheory_at_[hidden])
Date: 2010-02-25 10:44:05

Consider the following code, very simple in nature:

static const boost::gregorian::date windows_epoch_base(1601, 1, 1);

date_time d(windows_epoch_base, microseconds(12908391903991608));

This should resolve to sometime in early 2010

Now, the problem is that this number is already really big, not that many
factors of 10 away from the int64 overflow boundary.  microseconds() is
really just the subsecond_duration<> template, and on my machine it's being
parameterized as subsecond_duration<boost::posix_time::time_duration,
1000000>.  The code for the constructor is as follows:

explicit subsecond_duration(boost::int64_t ss)
 : base_duration(0,0,0, ss*traits_type::res_adjust() / frac_of_second)
{}

res_adjust is also resolving to 1000000.  So compiler is
doing 12908391903991608*res_adjust first, which causes an overflow.  I think
it should be doing ss * (traits_type::res_adjust() / frac_of_second)
instead.

I don't know a whole lot about date_time internals, so I thought I would ask
here before just submitting a bug.  Is the proposed fix correct?  I made the
change locally and it does indeed appear to resolve the problem.

Zach