id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
13109,Incorrect result when casting from multiprecision::uint128_t to unsigned long long.,gvisser@…,John Maddock,"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",Bugs,closed,To Be Determined,multiprecision,Boost 1.63.0,Problem,fixed,,