[Boost-users] [conversion] RoundEven odd behaviour

From: Vyacheslav E. Andrejev (vandrejev_at_[hidden])
Date: 2005-05-01 00:55:25

Hello All

I tried to use boost numeric conversion library and faced with strange feature 
of RoundEven that I can not comprehend or find expanation in the documentation. 
First I thought that this policy rounds float number to nearest integer, 
because RoundEven::round_style::value == std::round_to_nearest. But! This 
policy for example returns 2.0 for 3.0 as argument!

  cout << boost::numeric::converter<
      int
    , double
    , boost::numeric::conversion_traits<int, double>
    , boost::numeric::silent_overflow_handler
    , boost::numeric::RoundEven<double>
  >::convert(2.9) << endl;

  cout << boost::numeric::converter<
      int
    , double
    , boost::numeric::conversion_traits<int, double>
    , boost::numeric::silent_overflow_handler
    , boost::numeric::RoundEven<double>
  >::convert(3.0) << endl;

  cout << boost::numeric::converter<
      int
    , double
    , boost::numeric::conversion_traits<int, double>
    , boost::numeric::silent_overflow_handler
    , boost::numeric::RoundEven<double>
  >::convert(3.1) << endl;

Output of the program above will be:
3
2
3

What is the cause of such strange behaviour? This is a bug or there is something 
that I don't understand?

-- 
Vyacheslav E. Andrejev
System Architect, Excelsior, LLC