Method AppendDecimal64

rapidjson/internal/biginteger.h:224–232

private:
    void AppendDecimal64(const char* begin, const char* end) {
        uint64_t u = ParseUint64(begin, end);
        if (IsZero())
            *this = u;
        else {
            unsigned exp = static_cast<unsigned>(end - begin);
            (MultiplyPow5(exp) <<= exp) += u;   // *this = *this * 10^exp + u
        }
    }

    void PushBack(Type digit) {
        RAPIDJSON_ASSERT(count_ < kCapacity);