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

Subject: Re: [boost] [chrono] boost::chrono::floor() and negative durations
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-11-21 16:58:37

Le 21/11/13 21:23, Howard Hinnant a écrit :
> 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;
> }
>
You are right, as always. I will apply your suggestion.

Thanks,
Vicente