[Boost-users] [Chrono] Negative real time

Subject: [Boost-users] [Chrono] Negative real time
From: Wilfried Kirschenmann (wilfried.kirschenmann_at_[hidden])
Date: 2012-05-22 12:55:56

Dear chrono maintainer team,

Using the following example :

int main(int argc, char **argv)
{
       boost::chrono::process_real_cpu_clock::time_point start =
boost::chrono::process_real_cpu_clock::now();

       for ( long i = 0; i < 1000; ++i )  std::sqrt( 123.456L ); // burn
some time
       Sleep(10000); //idle some time

       boost::chrono::process_real_cpu_clock::time_point end =
boost::chrono::process_real_cpu_clock::now();
       std::cout << end << std::endl;

        boost::chrono::process_real_cpu_clock::duration elapsed = (end -
start);
       std::cout << "took real     : " << elapsed  << "nanoseconds\n";

       return 0;
}

I obtain negative times.

I run boost 1.49 win32 on Windows 7 x64 with Visual studio 2010.

Studying the behavior of the timer, I think that the error is one of these :
- process_real_cpu_clock::now() only stores the current time in a 32 bit
integer instead of a 64 bit integer
- time_points only prints the 32 lowest bits.
I came to this conclusion by observing the results printed before they got
negatives (printing in the loop with the sqrt): 2019000000 nanoseconds is
the last value printed before getting negative.

 Is there any mistake in my way of using this chronometer ?
Do you have a workaround ?

Thank you for your help !
Wilfried K.

-----
Cordialement,
Wilfried Kirschenmann

"An expert is a person who has made all the mistakes that can be made in a
very narrow field."*
*Niels Bohr - *Danish physicist (1885 - 1962)*