Endless loop in random.tcc (GCC 6.1.0) (may be a bug in Armadillo)

Question

I found that the C ++ 11 random number generator in GCC 6.1.0 causes codes stuck in Mac OS X 10.11.5, a simple piece of code looks like this:

#include <iostream> #include <armadillo> using namespace std; using namespace arma; int main(int argc, char const* argv[]) { cout << "check 1" << endl; cout << arma_rng::randn<double>() << endl; cout << "check 2" << endl; return 0; } 

I debugged this code with lldb and blocked the suspicious part in the random.tcc libstdc++ file:

 /** * Polar method due to Marsaglia. * * Devroye, L. Non-Uniform Random Variates Generation. Springer-Verlag, * New York, 1986, Ch. V, Sect. 4.4. */ template<typename _RealType> template<typename _UniformRandomNumberGenerator> typename normal_distribution<_RealType>::result_type normal_distribution<_RealType>:: operator()(_UniformRandomNumberGenerator& __urng, const param_type& __param) { result_type __ret; __detail::_Adaptor<_UniformRandomNumberGenerator, result_type> __aurng(__urng); if (_M_saved_available) { _M_saved_available = false; __ret = _M_saved; } else { result_type __x, __y, __r2; do { __x = result_type(2.0) * __aurng() - 1.0; __y = result_type(2.0) * __aurng() - 1.0; __r2 = __x * __x + __y * __y; } while (__r2 > 1.0 || __r2 == 0.0); const result_type __mult = std::sqrt(-2 * std::log(__r2) / __r2); _M_saved = __x * __mult; _M_saved_available = true; __ret = __y * __mult; } __ret = __ret * __param.stddev() + __param.mean(); return __ret; } 

where __aurng() always returns 0, so __r2 > 1.0 || __r2 == 0.0 __r2 > 1.0 || __r2 == 0.0 will never be executed.

UPDATE:

I found that this could be a bug in the Armadillo library, since I tried the following codes, which are in order:

 #include <iostream> #include <random> using namespace std; int main(int argc, const char *argv[]) { mt19937_64 rng; normal_distribution<double> dist; cout << dist(rng) << endl; return 0; }