Re: [Boost-bugs] [Boost C++ Libraries] #2737: Rounding failed for -0.5

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #2737: Rounding failed for -0.5
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-02-10 16:15:00

#2737: Rounding failed for -0.5
------------------------------------------+---------------------------------
  Reporter:  kennant.tom_at_[hidden]  |       Owner:  dgregor
      Type:  Bugs                         |      Status:  closed 
 Milestone:  Boost 1.38.0                 |   Component:  numeric
   Version:  Boost 1.37.0                 |    Severity:  Problem
Resolution:  invalid                      |    Keywords:         
------------------------------------------+---------------------------------

Comment(by steven_watanabe):

 The common method is not provided.
 Round to even has better statistical properties.
 It would look something like this based
 on RoundEven

 {{{
 template<class S>
 struct RoundCommon
 {
   typedef S source_type ;

   typedef typename mpl::if_< is_arithmetic<S>,S,S const&>::type
 argument_type ;

   static source_type nearbyint ( argument_type s )
   {
 #if !defined(BOOST_NO_STDC_NAMESPACE)
     using std::floor ;
     using std::ceil  ;
 #endif

     // only works inside the range not at the boundaries
     S prev = floor(s);
     S next = ceil(s);

     S rt = (s - prev) - (next - s); // remainder type

     S const zero(0.0);
     S const two(2.0);

     if ( rt < zero )
       return prev;
     else if ( rt > zero )
       return next;
     else if ( prev < zero )
       return prev;
     else
       return next;
   }

   typedef mpl::integral_c< std::float_round_style, std::round_to_nearest>
 round_style ;
 } ;
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/2737#comment:3>
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