Re: [boost] [chrono] boost::chrono::floor() and negative durations

Subject: Re: [boost] [chrono] boost::chrono::floor() and negative durations
From: Krzysztof Czainski (1czajnik_at_[hidden])
Date: 2013-11-21 17:14:37

2013/11/21 Krzysztof Czainski <1czajnik_at_[hidden]>

> 2013/11/21 Howard Hinnant <howard.hinnant_at_[hidden]>
>
>> On Nov 20, 2013, at 12:49 PM, Vicente J. Botet Escriba <
>> vicente.botet_at_[hidden]> wrote:
>>
>> > Le 20/11/13 13:45, Krzysztof Czainski a écrit :
>> >> Hello,
>> >>
>> >> The function boost::chrono::floor() is documented: "This function round
>> >> down the given parameter." Therefore I expect the assert in the
>> following
>> >> program to pass, but it fails:
>> >>
>> >> #include <boost/chrono/floor.hpp>
>> >> #include <cassert>
>> >>
>> >> int main()
>> >> {
>> >>     boost::chrono::nanoseconds const nsec( -1 );
>> >>     boost::chrono::seconds const sec =
>> >> boost::chrono::floor<boost::chrono::seconds>(nsec);
>> >>     assert( sec.count() == -1 );
>> >> }
>> >>
>> >> Is this intended behavior? If yes, could the docs be updated to clarify
>> >> this?
>> >>
>> >>
>> > Hi,
>> >
>> > no, there is a bug with negative numbers.
>> >
>> >     template <class To, class Rep, class Period>
>> >     To floor(const duration<Rep, Period>& d)
>> >     {
>> > +      if (d<duration<Rep, Period>::zero())
>> > +        return duration_cast<To>(d)-To(1);
>> > +      else
>> >         return duration_cast<To>(d);
>> >     }
>> >
>> > Please, coul dyou create a ticket so that I don't forget it.
>> >
>> > Thanks,
>> > Vicente
>> >
>> > _______________________________________________
>> > Unsubscribe & other changes:
>> http://lists.boost.org/mailman/listinfo.cgi/boost
>>
>> #include <chrono>
>>
>> using namespace std::chrono;
>>
>>     template <class To, class Rep, class Period>
>>     To floor(const duration<Rep, Period>& d)
>>     {
>>      if (d<duration<Rep, Period>::zero())
>>        return duration_cast<To>(d)-To(1);
>>      else
>>         return duration_cast<To>(d);
>>     }
>>
>> #include <iostream>
>>
>> int
>> main()
>> {
>>     using namespace std::literals;
>>     std::cout << floor<seconds>(-1000ms).count() << '\n';
>> }
>>
>> For me outputs:
>>
>> -2
>>
>> How about this instead:
>>
>> template <class To, class Rep, class Period>
>> To
>> floor(const std::chrono::duration<Rep, Period>& d)
>> {
>>     To t = std::chrono::duration_cast<To>(d);
>>     if (t > d)
>>         --t;
>>     return t;
>> }
>>
>> Howard
>
>
> Ticket #9419 created.
>
> I think it's a bit more complicated. Doesn't Howard's version return -2 as
> well?
>

Oh, I get it now, clever ;)

Regards,
Kris