[Boost-users] boost::rational does not maintain its invariant in case of overflow

Subject: [Boost-users] boost::rational does not maintain its invariant in case of overflow
From: Frédéric (ufospoke_at_[hidden])
Date: 2018-04-11 13:11:05

With the program shown below, I obtained the following output:
std::numeric_limits<long>::max() == 9223372036854775807
r == boost::rational<long>(4294967296, 1853020188851841) ==
4294967296/1853020188851841
r * r == 0/8733086111712066817

Clearly there are 2 overflows but this leads to the invariant of the
class not being maintained, i.e. the faction is not simplified to 0/1
(gcd(num, den) != 1).

F

#include <boost/rational.hpp>

#include <iostream>

int main() {
  std::cout << "std::numeric_limits<long>::max() == "
            << std::numeric_limits<long>::max() << '\n';
  boost::rational<long> r(4294967296, 1853020188851841);
  std::cout << "r == boost::rational<long>(4294967296, 1853020188851841) == "
            << r << '\n';
  std::cout << "r * r == " << (r * r) << '\n';
  return 0;
}