Re: [Boost-users] [Rational] "r.den > zero" assertion failure

Subject: Re: [Boost-users] [Rational] "r.den > zero" assertion failure
From: Michael Olea (oleaj_at_[hidden])
Date: 2011-07-13 10:25:08

On Jul 13, 2011, at 2:16 AM, Pierre Cagne wrote:

> Hi,
> 
> I'm having a weird dynamic failure using Boost.Rational.
> Using some rationals and doing a calculus, i'm ending with a rational with a negative denominator, and so unusable for comparison (hence the r.den > 0 assertion failure during the execution).
> 
> More precisely, here is a piece of code : (with typedef boost::rational<mpz_class> rat)
>  std::cout << xa << " " << ya << " "
> 	          << xb << " " << yb << " "
> 	          << xc << " " << yc << " "
> 	          << xd << " " << yd << std::endl;
>  // determinant
>  rat delta = (xb - xa)*(yc - yd) - (yb - ya)*(xc - xd);
>  std::cout << "Delta : " << delta << std::endl;
>  /* ... some comparisons on delta ...*/
> 
> For the following result :
>  0/1 1/4 1/2 0/1 0/1 0/1 1/1 0/1
>  Delta : 1/-4
>  Assertion failed: (r.den > zero), function operator<, file /usr/local/include/boost/rational.hpp, line 388.
> 
> How does it come that Boost does not maintain the assertion correct ? I precise that the same code with the type boost::rational<int> does not produce the failure.
> 
> Thankfully.
> 
> 
> P.S. : i'm new on this mailing-list ; does my message match with the common pattern of this list ?
> --
> Pierre Cagne
> pierre.cagne_at_[hidden]

My guess is that you are getting an integer overflow of the underlying integer type.