[Boost-bugs] [Boost C++ Libraries] #9925: operators_test.cpp test_left_shiftable is failing due to invalid parameters

Subject: [Boost-bugs] [Boost C++ Libraries] #9925: operators_test.cpp test_left_shiftable is failing due to invalid parameters
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-04-18 18:28:38

#9925: operators_test.cpp test_left_shiftable is failing due to invalid parameters
------------------------------+--------------------------------
 Reporter:  chris.cooper@…    |      Owner:  grafik
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  Regression Testing
  Version:  Boost 1.54.0      |   Severity:  Problem
 Keywords:                    |
------------------------------+--------------------------------
 In libs/utility/operators_test.cpp, test_left_shiftable is checking
 whether one random value shifted by a second random value, is the same
 whether called directly or via the Wrapper2<> and Wrapper1<> template
 classes.

 However, according to C++ ISO specification (INCITS/ISO/IEC
 14882-2011\[2012\]), section 5.8.2 (which I don't have, but is referenced
 at http: / / msdn.microsoft.com/en-us/library/336xbhcz.aspx), left-
 shifting a signed value has undefined behavior (which is much more
 unpleasant than implementation-defined behavior) if the result doesn't fit
 in an unsigned value of the same size.

 With the clang compiler that comes with Xcode 5.1 ("Apple LLVM version 5.1
 (clang-503.0.38) (based on LLVM 3.4svn)"), the results of such left-shifts
 are seemingly random - this code:

 {{{
 long b1 = 48271;
 int s = 1291394886;
 std::cout << (b1 << s) << std::endl;
 std::cout << (b1 << s)<< std::endl;
 std::cout << (b1 << s)<< std::endl;
 }}}


 prints three different numbers.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9925>
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