Class BigInteger

rapidjson/internal/biginteger.h:28–285

namespace internal {

class BigInteger {
public:
    typedef uint64_t Type;

    BigInteger(const BigInteger& rhs) : count_(rhs.count_) {
        std::memcpy(digits_, rhs.digits_, count_ * sizeof(Type));
    }

    explicit BigInteger(uint64_t u) : count_(1) {
        digits_[0] = u;
    }

    BigInteger(const char* decimals, size_t length) : count_(1) {
        RAPIDJSON_ASSERT(length > 0);
        digits_[0] = 0;
        size_t i = 0;
        const size_t kMaxDigitPerIteration = 19;  // 2^64 = 18446744073709551616 > 10^19
        while (length >= kMaxDigitPerIteration) {
            AppendDecimal64(decimals + i, decimals + i + kMaxDigitPerIteration);
            length -= kMaxDigitPerIteration;
            i += kMaxDigitPerIteration;
        }

        if (length > 0)
            AppendDecimal64(decimals + i, decimals + i + length);
    }
    
    BigInteger& operator=(const BigInteger &rhs)
    {
        if (this != &rhs) {
            count_ = rhs.count_;
            std::memcpy(digits_, rhs.digits_, count_ * sizeof(Type));
        }
        return *this;
    }
    
    BigInteger& operator=(uint64_t u) {
        digits_[0] = u;            
        count_ = 1;
        return *this;
    }

    BigInteger& operator+=(uint64_t u) {
        Type backup = digits_[0];
        digits_[0] += u;
        for (size_t i = 0; i < count_ - 1; i++) {
            if (digits_[i] >= backup)
                return *this; // no carry
            backup = digits_[i + 1];
            digits_[i + 1] += 1;
        }

        // Last carry
        if (digits_[count_ - 1] < backup)
            PushBack(1);

        return *this;
    }