Re: [Boost-bugs] [Boost C++ Libraries] #12330: boost::thread starts with invalid FPU control word value in Embarcadero C++ Builder

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #12330: boost::thread starts with invalid FPU control word value in Embarcadero C++ Builder
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2017-01-03 08:00:47

#12330: boost::thread starts with invalid FPU control word value in Embarcadero C++
Builder
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  Reporter:  Ville-Valtteri Tiittanen <ville-    |      Owner:  viboes
  valtteri.tiittanen@…>                          |     Status:  assigned
      Type:  Bugs                                |  Component:  thread
 Milestone:  To Be Determined                    |   Severity:  Regression
   Version:  Boost 1.55.0                        |   Keywords:
Resolution:                                      |
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Comment (by Ville-Valtteri Tiittanen):

 Replying to [comment:7 viboes]:
 > I have no idea what does it means in terms of the standard interface
 that the parent thread  should inherit floating point control word.
 >
 > Please could you point me where
 > "C++ standard specifies that floating point control word should be
 inherited from the parent thread." is specified?

 The C Standard (ISO/IEC 9899:2011) has this statement in 7.6 paragraph 2:

     The floating-point environment has thread storage duration. The
 initial state for a thread’s floating-point environment is the current
 state of the floating-point environment of the thread that creates it at
 the time of creation.

 The C++ Standard (ISO/IEC 14882:2014) has this statement in 26.3.1
 [cfenv.syn] paragraph 3:

     The floating-point environment has thread storage duration (3.7.2).
 The initial state for a thread’s floatingpoint environment is the state of
 the floating-point environment of the thread that constructs the
 corresponding std::thread object (30.3.1) at the time it constructed the
 object.

 So to match behavior of std::thread as defined by standard, a thread
 object should save the state of floating point environment at the
 beginning of constructor, and restore that environment in the new thread
 after it has been started.

 There is a C++ interface for floating point environment
 (http://en.cppreference.com/w/cpp/numeric/fenv), but I do not know if that
 includes everything that can be changed with _control87().

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12330#comment:8>
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