[Boost-users] [date_time] absolute value for time_duration?

From: Michael Fawcett (michael.fawcett_at_[hidden])
Date: 2007-11-09 12:46:55

What is the best way to ensure that one has a positive time_duration?
I'm dealing with hundreds of thousands of data points and need to
gather the points that are temporally near a given time (based on a
duration).  For example, find all points in the collection that are
within 1 hour of Feb 2, 5:00pm.  I used the following code to verify
that simply multiplying by -1 would give the desired result, but it
would probably be nicer to provide a std::abs overload.

        boost::posix_time::ptime lhs1(boost::gregorian::date(2007, 2, 1),
boost::posix_time::hours(1));
        boost::posix_time::ptime rhs1(boost::gregorian::date(2007, 2, 2),
boost::posix_time::hours(1));
        boost::posix_time::time_duration elapsed1 = lhs1 - rhs1;
        elapsed1 *= -1;

        boost::posix_time::ptime lhs2(boost::gregorian::date(2007, 2, 2),
boost::posix_time::hours(1));
        boost::posix_time::ptime rhs2(boost::gregorian::date(2007, 2, 1),
boost::posix_time::hours(1));
        boost::posix_time::time_duration elapsed2 = lhs2 - rhs2;

        assert(elapsed1 == elapsed2);

and the actual code is something like (where duration would be 1 hour
in this example):

        boost::posix_time::time_duration elapsed = pt.timestamp - rhs.timestamp;
        if (elapsed.is_negative())
                elapsed *= -1;
        return elapsed <= duration;

I realize that one could also use std::max and std::min, but that
seems a bit inefficient, especially since this is a very performance
critical area of our application.

Thanks,

--Michael Fawcett