Method parse

include/boost/parser/detail/numeric.hpp:676–802

    {
        template <typename Iterator, typename Sentinel, typename Attribute>
        static bool
        parse(Iterator& first, Sentinel last, Attribute& attr,
            RealPolicies const& p)
        {
            if (first == last)
                return false;
            Iterator save = first;

            // Start by parsing the sign. neg will be true if
            // we got a "-" sign, false otherwise.
            bool neg = p.parse_sign(first, last);

            // Now attempt to parse an integer
            T n = 0;
            bool got_a_number = p.parse_n(first, last, n);

            // If we did not get a number it might be a NaN, Inf or a leading
            // dot.
            if (!got_a_number)
            {
                // Check whether the number to parse is a NaN or Inf
                if (p.parse_nan(first, last, n) ||
                    p.parse_inf(first, last, n))
                {
                    // If we got a negative sign, negate the number
                    attr = detail_spirit_x3::negate(neg, n);
                    return true;    // got a NaN or Inf, return early
                }

                // If we did not get a number and our policies do not
                // allow a leading dot, fail and return early (no-match)
                if (!p.allow_leading_dot)
                {
                    first = save;
                    return false;
                }
            }

            bool e_hit = false;
            Iterator e_pos;
            int frac_digits = 0;

            // Try to parse the dot ('.' decimal point)
            if (p.parse_dot(first, last))
            {
                // We got the decimal point. Now we will try to parse
                // the fraction if it is there. If not, it defaults
                // to zero (0) only if we already got a number.
                Iterator savef = first;
                if (p.parse_frac_n(first, last, n))
                {
                    // Optimization note: don't compute frac_digits if T is
                    // an unused_type. This should be optimized away by the compiler.
                    if (!std::is_same_v<T, unused_type>)
                        frac_digits =
                            static_cast<int>(std::distance(savef, first));
                    BOOST_PARSER_DEBUG_ASSERT(frac_digits >= 0);
                }