boost::rational does not maintain its invariant in case of overflow
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; }
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 <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; }
safe_numerics can address this. Robert Ramey
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