I'm getting some strange crashes when I try to compare mp_ints with native types. The code below is sufficient to reproduce it: #include <stdint.h> #include <iostream> #include <boost/mp_math/mp_int.hpp> using namespace boost::mp_math; using namespace std; int main() { mp_int<> a = mp_int<>("0x100000000"); cout << (1 < a) << endl; return 0; } The problem appears to be the definition of integral_ops_impl<..., true>::q (i.e., for signed IntegralT): static const typename MpInt::size_type q = std::numeric_limits<IntegralT>::digits + (MpInt::valid_bits - 1) / MpInt::valid_bits; In the case where IntegralT=int32_t and digit_type=uint32_t, q is 31. Contrast this with the definition for unsigned IntegralT: static const typename MpInt::size_type q = std::numeric_limits<IntegralT>::digits / (MpInt::valid_bits + 1) + 1; When IntegralT=uint32_t and digit_type=uint32_t, q is 1. The overflow of operator< comes because the check that verifies that the MpInt can't fit in an IntegralT is (condition (lhs.size() > q). This fails for q=31. If the definition of q had the first line parenthesized: static const typename MpInt::size_type q = (std::numeric_limits<IntegralT>::digits + MpInt::valid_bits - 1) / MpInt::valid_bits; then q would be 1, and the code branch with the overflow would not be taken. -- Nathan