Function grisu2_round

native/thirdpart/json/json.hpp:13190–13225

}

inline void grisu2_round(char* buf, int len, std::uint64_t dist, std::uint64_t delta,
                         std::uint64_t rest, std::uint64_t ten_k)
{
    assert(len >= 1);
    assert(dist <= delta);
    assert(rest <= delta);
    assert(ten_k > 0);

    //               <--------------------------- delta ---->
    //                                  <---- dist --------->
    // --------------[------------------+-------------------]--------------
    //               M-                 w                   M+
    //
    //                                  ten_k
    //                                <------>
    //                                       <---- rest ---->
    // --------------[------------------+----+--------------]--------------
    //                                  w    V
    //                                       = buf * 10^k
    //
    // ten_k represents a unit-in-the-last-place in the decimal representation
    // stored in buf.
    // Decrement buf by ten_k while this takes buf closer to w.

    // The tests are written in this order to avoid overflow in unsigned
    // integer arithmetic.

    while (rest < dist
            and delta - rest >= ten_k
            and (rest + ten_k < dist or dist - rest > rest + ten_k - dist))
    {
        assert(buf[len - 1] != '0');
        buf[len - 1]--;
        rest += ten_k;
    }
}

/*!
Generates V = buffer * 10^decimal_exponent, such that M- <= V <= M+.