[Boost-bugs] [Boost C++ Libraries] #11054: Floating-point comparison of multiprecision values fails if expression template is on

Subject: [Boost-bugs] [Boost C++ Libraries] #11054: Floating-point comparison of multiprecision values fails if expression template is on
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-02-24 12:23:08

#11054: Floating-point comparison of multiprecision values fails if expression
template is on
-----------------------------------------------------+---------------------
 Reporter:  pbristow                                 |      Owner:  rogeeff
     Type:  Bugs                                     |     Status:  new
Milestone:  To Be Determined                         |  Component:  test
  Version:  Boost 1.58.0                             |   Severity:  Problem
 Keywords:  test multiprecision expression template  |
-----------------------------------------------------+---------------------
 Floating-point comparison of multiprecision values fails if expression
 template option is
 on (which is the default for example with
 {{{
 boost::multiprecision::cpp_bin_float_50;

 typedef
 boost::multiprecision::number<boost::multiprecision::cpp_bin_float<50>,
   boost::multiprecision::et_on>
   cpp_bin_float_50_et_on;  // et_on is default so is same as
 cpp_bin_float_50.)
 }}}

 The error appears inside Boost.test floating_point_comparision.hpp at an
 apparently impossible place fpc_detail::fpt_abs.

 The actual problem is in class close_at_tolerance operator() line 204

 {{{
    FPT diff = fpc_detail::fpt_abs(left - right);
 }}}
 in order to allow use of expression templates, it is necessary to cast the
 variable diff to the FPT explicitly, thus:
 {{{
    FPT diff = fpc_detail::fpt_abs( static_cast<FPT>(left - right) );
 }}}

 I can provide an explicit test for this, but it seems such a trivial
 change.

 This change is vital to allow Boost.Test to be used fully with
 Boost.Multiprecision.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11054>
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