When calling export_bits on a negative boost::multiprecision number based on cpp_int, an exception is thrown from the internal method msb ("testing individual bits in negative values is not supported"). (Boost 1.60)
boost::multiprecision::checked_int128_t i (-1); // use negative number
std::vector<unsigned char> v;
export_bits(i, std::back_inserter(v), 8); // throws
How can I extract the content of a boost::multiprecision number? Boost documentation says, export_bits is designed to be used for data exchange, so in my understanding it would be a major flaw, if it cannot export supported values.
I learnt that a workaround might be to directly access the backend's limbs, but it is accessing internals that may change.
Update: I posted the question on the boost mailinglist, opened a ticket for this https://svn.boost.org/trac/boost/ticket/12170, and it will be fixed in an upcoming release.
