Boost Users :
Subject: Re: [Boost-users] [Rational] "r.den > zero" assertion failure
From: Michael Olea (oleaj_at_[hidden])
Date: 2011-07-13 10:31:41
On Jul 13, 2011, at 2:16 AM, Pierre Cagne wrote:
> 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.
> P.S. : i'm new on this mailing-list ; does my message match with the common pattern of this list ?
> Pierre Cagne
> My guess is that you are getting an integer overflow of the underlying integer type.
Sorry. I overlooked that the integer type is mpz_class.
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