Assertation on big exponents

RandomInEqualities commented 5 years ago

The following code:

#include <boost/spirit/home/x3.hpp>

#include <string>

namespace x3 = boost::spirit::x3;

int main() {
  const std::string expression = "1e310";
  auto start = expression.cbegin();
  auto end = expression.cend();
  double result;
  x3::phrase_parse(start, end, x3::double_, x3::space, result);
  return 0;
}

Asserts in pow10.hpp:

Assertion failed: dim < sizeof(exponents)/sizeof(double), file boost/spirit/home/x3/support/numeric_utils/pow10.hpp, line 85

Due to the exponentiation table only holding 308 values. In qi the expression is rejected.

One can use their own real policy to workaround it:

template<typename T>
struct RealPolicy : x3::ureal_policies<T> {
    template<typename Iterator>
    static bool parse_exp_n(Iterator& first, Iterator const& last, int& attr_) {
        // boost spirit asserts/reads out of bounds when |exponent| is larger than 308
        const Iterator save = first;
        if (x3::ureal_policies<T>::parse_exp_n(first, last, attr_)) {
            if (attr_ >= -308 && attr_ <= 308) {
                return true;
            } else {
                first = save;
                return false;
            }
        }
        return false;
    }
};
x3::real_parser<double, RealPolicy<double>> const double_ = {};