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

11 Apr 2018


      On 4/11/18 6:11 AM, Frédéric via Boost-users wrote:
...
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 
#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;
}
safe_numerics can address this.

Robert Ramey