Re: [Boost-bugs] [Boost C++ Libraries] #5758: Boost.Test Floating-point comparison diagnostic output does not support radix 10

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5758: Boost.Test Floating-point comparison diagnostic output does not support radix 10
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-07-09 13:50:10

#5758: Boost.Test Floating-point comparison diagnostic output does not support
radix 10
--------------------------------------+-------------------------------------
  Reporter:  pbristow                 |       Owner:  rogeeff                                  
      Type:  Support Requests         |      Status:  closed                                   
 Milestone:  Boost 1.48.0             |   Component:  test                                     
   Version:  Boost Development Trunk  |    Severity:  Problem                                  
Resolution:  fixed                    |    Keywords:  floating point radix 10 decimal precision
--------------------------------------+-------------------------------------

Comment (by pbristow):

 Using John Maddock and Christopher Kormanyos mutliprecision currently
 under review

 BOOST_AUTO_TEST_CASE(cpp_loopback_test_message)
 { // Loopback.
   using namespace boost::multiprecision;

   cpp_dec_float_100 a = "1.";
   cpp_dec_float_100 b = "1.";
   b += 1e-100;

   BOOST_CHECK_EQUAL(a, b);
 } // BOOST_AUTO_TEST_CASE(cpp_loopback_test_message)

 Gives this misleading message

 error : in "cpp_loopback_test_message": check a == b failed [1 != 1]

         else if ( std::numeric_limits<T>::is_specialized &&
 std::numeric_limits<T>::radix == 10 )

 // adding this to cater for radix 10
         {
 #ifdef BOOST_NO_NUMERIC_LIMITS_LOWEST
 // No support for std::numeric_limits<double>::max_digits10;
 // so guess that a couple of guard digits more than digits10 will display
 any difference.
            ostr.precision( 2 + std::numeric_limits<T>::digits10 );
 #else
   // std::numeric_limits<double>::max_digits10; IS supported.
   // Any noisy or guard digits needed to display any difference are
 included in max_digits10.
            ostr.precision( std::numeric_limits<T>::max_digits10 );
 #endif
        }
        // else if T is not specialized, then will just get the default
 precision of 6 digits.

 gives this more helpful mesage

 in "cpp_loopback_test_message": check a == b failed [1 !=
 1.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000001999]

  BOOST_NO_NUMERIC_LIMITS_LOWEST is a proxy for support of max_digits10.

 And seems to work in tests using Boost.Math.

 At present only MSVC 10 and some gcc test platforms support max_digits10.

 Sandia clang darwin trunk c++11 seems to fail with and without check for
 BOOST_NO_NUMERIC_LIMITS_LOWEST.

 Please tell me immediately of any problem this revised version causes.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5758#comment:6>
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