[Boost-bugs] [Boost C++ Libraries] #13109: Incorrect result when casting from multiprecision::uint128_t to unsigned long long.

Subject: [Boost-bugs] [Boost C++ Libraries] #13109: Incorrect result when casting from multiprecision::uint128_t to unsigned long long.
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2017-07-07 01:54:31

#13109: Incorrect result when casting from multiprecision::uint128_t to unsigned
long long.
------------------------------+----------------------------
 Reporter:  gvisser@…         |      Owner:  John Maddock
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  multiprecision
  Version:  Boost 1.63.0      |   Severity:  Problem
 Keywords:                    |
------------------------------+----------------------------
 I found in Boost 1.63.0 on:
 Ubuntu 14.04.5 with g++ (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4,
 64-bit Windows 10's Windows Subsystem for Linux with g++ (Ubuntu
 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609.

 code snippet:
 uint128_t b128 = 0xFFFFFFFFFFFFFFFFFFFFFFFFC0A800FF_cppui;
 unsigned long long ull( static_cast<unsigned long long>( b128 ) );
 printf( "ull: %016llX\n", ull );

 The output is:
 ull: FFFFFFFFFFFFFFFF

 Under Windows 10 and Visual Studio 2015 the output is:
 ull: FFFFFFFFC0A800FF

 The work around I'm using is to mask out the upper 64 bits:
 ull = static_cast<unsigned long long>(b128 & 0x0FFFFFFFFFFFFFFFF);

 Thanks,
 Gary Visser

-- 
Ticket URL: <https://svn.boost.org/trac10/boost/ticket/13109>
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