BigInt.hpp

/*
    BigInt
    ------
    Arbitrary-sized integer class for C++.
    
    Version: 0.4.0-dev
    Released on: 03 January 2018 10:51 IST
    Author: Syed Faheel Ahmad (faheel@live.in)
    Project on GitHub: https://github.com/faheel/BigInt
    License: MIT
*/

/*
    ===========================================================================
    BigInt
    ===========================================================================
    Definition for the BigInt class.
*/

/*
MIT License
Copyright (c) 2017 - 2018 Syed Faheel Ahmad
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

#ifndef BIG_INT_HPP
#define BIG_INT_HPP

#include <iostream>

class BigInt {
    std::string value;
    char sign;

    public:
        // Constructors:
        BigInt();
        BigInt(const BigInt&);
        BigInt(const long long&);
        BigInt(const std::string&);

        // Assignment operators:
        BigInt& operator=(const BigInt&);
        BigInt& operator=(const long long&);
        BigInt& operator=(const std::string&);

        // Unary arithmetic operators:
        BigInt operator+() const;   // unary +
        BigInt operator-() const;   // unary -

        // Binary arithmetic operators:
        BigInt operator+(const BigInt&) const;
        BigInt operator-(const BigInt&) const;
        BigInt operator*(const BigInt&) const;
        BigInt operator/(const BigInt&) const;
        BigInt operator%(const BigInt&) const;
        BigInt operator+(const long long&) const;
        BigInt operator-(const long long&) const;
        BigInt operator*(const long long&) const;
        BigInt operator/(const long long&) const;
        BigInt operator%(const long long&) const;
        BigInt operator+(const std::string&) const;
        BigInt operator-(const std::string&) const;
        BigInt operator*(const std::string&) const;
        BigInt operator/(const std::string&) const;
        BigInt operator%(const std::string&) const;

        // Arithmetic-assignment operators:
        BigInt& operator+=(const BigInt&);
        BigInt& operator-=(const BigInt&);
        BigInt& operator*=(const BigInt&);
        BigInt& operator/=(const BigInt&);
        BigInt& operator%=(const BigInt&);
        BigInt& operator+=(const long long&);
        BigInt& operator-=(const long long&);
        BigInt& operator*=(const long long&);
        BigInt& operator/=(const long long&);
        BigInt& operator%=(const long long&);
        BigInt& operator+=(const std::string&);
        BigInt& operator-=(const std::string&);
        BigInt& operator*=(const std::string&);
        BigInt& operator/=(const std::string&);
        BigInt& operator%=(const std::string&);

        // Increment and decrement operators:
        BigInt& operator++();       // pre-increment
        BigInt& operator--();       // pre-decrement
        BigInt operator++(int);     // post-increment
        BigInt operator--(int);     // post-decrement

        // Relational operators:
        bool operator<(const BigInt&) const;
        bool operator>(const BigInt&) const;
        bool operator<=(const BigInt&) const;
        bool operator>=(const BigInt&) const;
        bool operator==(const BigInt&) const;
        bool operator!=(const BigInt&) const;
        bool operator<(const long long&) const;
        bool operator>(const long long&) const;
        bool operator<=(const long long&) const;
        bool operator>=(const long long&) const;
        bool operator==(const long long&) const;
        bool operator!=(const long long&) const;
        bool operator<(const std::string&) const;
        bool operator>(const std::string&) const;
        bool operator<=(const std::string&) const;
        bool operator>=(const std::string&) const;
        bool operator==(const std::string&) const;
        bool operator!=(const std::string&) const;

        // I/O stream operators:
        friend std::istream& operator>>(std::istream&, BigInt&);
        friend std::ostream& operator<<(std::ostream&, const BigInt&);

        // Conversion functions:
        std::string to_string() const;
        int to_int() const;
        long to_long() const;
        long long to_long_long() const;
};

#endif  // BIG_INT_HPP


/*
    ===========================================================================
    Utility functions
    ===========================================================================
*/

#ifndef BIG_INT_UTILITY_FUNCTIONS_HPP
#define BIG_INT_UTILITY_FUNCTIONS_HPP

#include <tuple>


/*
    is_valid_number
    ---------------
    Checks whether the given string is a valid integer.
*/

bool is_valid_number(const std::string& num) {
    for (char digit : num)
        if (digit < '0' or digit > '9')
            return false;

    return true;
}


/*
    strip_leading_zeroes
    --------------------
    Strip the leading zeroes from a number represented as a string.
*/

void strip_leading_zeroes(std::string& num) {
    size_t i;
    for (i = 0; i < num.size(); i++)
        if (num[i] != '0')
            break;

    if (i == num.size())
        num = "0";
    else
        num = num.substr(i);
}


/*
    add_leading_zeroes
    ------------------
    Adds a given number of leading zeroes to a string-represented integer `num`.
*/

void add_leading_zeroes(std::string& num, size_t num_zeroes) {
    num = std::string(num_zeroes, '0') + num;
}


/*
    add_trailing_zeroes
    -------------------
    Adds a given number of trailing zeroes to a string-represented integer `num`.
*/

void add_trailing_zeroes(std::string& num, size_t num_zeroes) {
    num += std::string(num_zeroes, '0');
}


/*
    get_larger_and_smaller
    ----------------------
    Identifies the given string-represented integers as `larger` and `smaller`,
    padding the smaller number with leading zeroes to make it equal in length to
    the larger number.
*/

std::tuple<std::string, std::string> get_larger_and_smaller(const std::string& num1,
        const std::string& num2) {
    std::string larger, smaller;
    if (num1.size() > num2.size() or
        (num1.size() == num2.size() and num1 > num2)) {
        larger = num1;
        smaller = num2;
    }
    else {
        larger = num2;
        smaller = num1;
    }

    // pad the smaller number with zeroes
    add_leading_zeroes(smaller, larger.size() - smaller.size());

    return std::make_tuple(larger, smaller);
}

#endif  // BIG_INT_UTILITY_FUNCTIONS_HPP


/*
    ===========================================================================
    Constructors
    ===========================================================================
*/

#ifndef BIG_INT_CONSTRUCTORS_HPP
#define BIG_INT_CONSTRUCTORS_HPP



/*
    Default constructor
    -------------------
*/

BigInt::BigInt() {
    value = "0";
    sign = '+';
}


/*
    Copy constructor
    ----------------
*/

BigInt::BigInt(const BigInt& num) {
    value = num.value;
    sign = num.sign;
}


/*
    Integer to BigInt
    -----------------
*/

BigInt::BigInt(const long long& num) {
    value = std::to_string(num);
    if (num < 0) {
        sign = '-';
        value = value.substr(1);    // remove minus sign from value
    }
    else
        sign = '+';
}


/*
    String to BigInt
    ----------------
*/

BigInt::BigInt(const std::string& num) {
    if (num[0] == '+' or num[0] == '-') {     // check for sign
        std::string magnitude = num.substr(1);
        if (is_valid_number(magnitude)) {
            value = magnitude;
            sign = num[0];
        }
        else {
            throw std::invalid_argument("Expected an integer, got \'" + num + "\'");
        }
    }
    else {      // if no sign is specified
        if (is_valid_number(num)) {
            value = num;
            sign = '+';    // positive by default
        }
        else {
            throw std::invalid_argument("Expected an integer, got \'" + num + "\'");
        }
    }
    strip_leading_zeroes(value);
}

#endif  // BIG_INT_CONSTRUCTORS_HPP


/*
    ===========================================================================
    Conversion functions for BigInt
    ===========================================================================
*/

#ifndef BIG_INT_CONVERSION_FUNCTIONS_HPP
#define BIG_INT_CONVERSION_FUNCTIONS_HPP


/*
    to_string
    ---------
    Converts a BigInt to a string.
*/

std::string BigInt::to_string() const {
    // prefix with sign if negative
    return this->sign == '-' ? "-" + this->value : this->value;
}


/*
    to_int
    ------
    Converts a BigInt to an int.
    NOTE: If the BigInt is out of range of an int, stoi() will throw an
    out_of_range exception.
*/

int BigInt::to_int() const {
    return std::stoi(this->to_string());
}


/*
    to_long
    -------
    Converts a BigInt to a long int.
    NOTE: If the BigInt is out of range of a long int, stol() will throw an
    out_of_range exception.
*/

long BigInt::to_long() const {
    return std::stol(this->to_string());
}


/*
    to_long_long
    ------------
    Converts a BigInt to a long long int.
    NOTE: If the BigInt is out of range of a long long int, stoll() will throw
    an out_of_range exception.
*/

long long BigInt::to_long_long() const {
    return std::stoll(this->to_string());
}

#endif  // BIG_INT_CONVERSION_FUNCTIONS_HPP


/*
    ===========================================================================
    Assignment operators
    ===========================================================================
*/

#ifndef BIG_INT_ASSIGNMENT_OPERATORS_HPP
#define BIG_INT_ASSIGNMENT_OPERATORS_HPP



/*
    BigInt = BigInt
    ---------------
*/

BigInt& BigInt::operator=(const BigInt& num) {
    value = num.value;
    sign = num.sign;

    return *this;
}


/*
    BigInt = Integer
    ----------------
*/

BigInt& BigInt::operator=(const long long& num) {
    BigInt temp(num);
    value = temp.value;
    sign = temp.sign;

    return *this;
}


/*
    BigInt = String
    ---------------
*/

BigInt& BigInt::operator=(const std::string& num) {
    BigInt temp(num);
    value = temp.value;
    sign = temp.sign;

    return *this;
}

#endif  // BIG_INT_ASSIGNMENT_OPERATORS_HPP


/*
    ===========================================================================
    Unary arithmetic operators
    ===========================================================================
*/

#ifndef BIG_INT_UNARY_ARITHMETIC_OPERATORS_HPP
#define BIG_INT_UNARY_ARITHMETIC_OPERATORS_HPP



/*
    +BigInt
    -------
    Returns the value of a BigInt.
    NOTE: This function does not return the absolute value. To get the absolute
    value of a BigInt, use the `abs` function.
*/

BigInt BigInt::operator+() const {
    return *this;
}


/*
    -BigInt
    -------
    Returns the negative of a BigInt.
*/

BigInt BigInt::operator-() const {
    BigInt temp;

    temp.value = value;
    if (value != "0") {
        if (sign == '+')
            temp.sign = '-';
        else
            temp.sign = '+';
    }

    return temp;
}

#endif  // BIG_INT_UNARY_ARITHMETIC_OPERATORS_HPP


/*
    ===========================================================================
    Relational operators
    ===========================================================================
    All operators depend on the '<' and/or '==' operator(s).
*/

#ifndef BIG_INT_RELATIONAL_OPERATORS_HPP
#define BIG_INT_RELATIONAL_OPERATORS_HPP



/*
    BigInt == BigInt
    ----------------
*/

bool BigInt::operator==(const BigInt& num) const {
    return (sign == num.sign) and (value == num.value);
}


/*
    BigInt != BigInt
    ----------------
*/

bool BigInt::operator!=(const BigInt& num) const {
    return !(*this == num);
}


/*
    BigInt < BigInt
    ---------------
*/

bool BigInt::operator<(const BigInt& num) const {
    if (sign == num.sign) {
        if (sign == '+') {
            if (value.length() == num.value.length())
                return value < num.value;
            else
                return value.length() < num.value.length();
        }
        else
            return -(*this) > -num;
    }
    else
        return sign == '-';
}


/*
    BigInt > BigInt
    ---------------
*/

bool BigInt::operator>(const BigInt& num) const {
    return !((*this < num) or (*this == num));
}


/*
    BigInt <= BigInt
    ----------------
*/

bool BigInt::operator<=(const BigInt& num) const {
    return (*this < num) or (*this == num);
}


/*
    BigInt >= BigInt
    ----------------
*/

bool BigInt::operator>=(const BigInt& num) const {
    return !(*this < num);
}


/*
    BigInt == Integer
    -----------------
*/

bool BigInt::operator==(const long long& num) const {
    return *this == BigInt(num);
}


/*
    Integer == BigInt
    -----------------
*/

bool operator==(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) == rhs;
}


/*
    BigInt != Integer
    -----------------
*/

bool BigInt::operator!=(const long long& num) const {
    return !(*this == BigInt(num));
}


/*
    Integer != BigInt
    -----------------
*/

bool operator!=(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) != rhs;
}


/*
    BigInt < Integer
    ----------------
*/

bool BigInt::operator<(const long long& num) const {
    return *this < BigInt(num);
}


/*
    Integer < BigInt
    ----------------
*/

bool operator<(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) < rhs;
}


/*
    BigInt > Integer
    ----------------
*/

bool BigInt::operator>(const long long& num) const {
    return *this > BigInt(num);
}


/*
    Integer > BigInt
    ----------------
*/

bool operator>(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) > rhs;
}


/*
    BigInt <= Integer
    -----------------
*/

bool BigInt::operator<=(const long long& num) const {
    return !(*this > BigInt(num));
}


/*
    Integer <= BigInt
    -----------------
*/

bool operator<=(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) <= rhs;
}


/*
    BigInt >= Integer
    -----------------
*/

bool BigInt::operator>=(const long long& num) const {
    return !(*this < BigInt(num));
}


/*
    Integer >= BigInt
    -----------------
*/

bool operator>=(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) >= rhs;
}


/*
    BigInt == String
    ----------------
*/

bool BigInt::operator==(const std::string& num) const {
    return *this == BigInt(num);
}


/*
    String == BigInt
    ----------------
*/

bool operator==(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) == rhs;
}


/*
    BigInt != String
    ----------------
*/

bool BigInt::operator!=(const std::string& num) const {
    return !(*this == BigInt(num));
}


/*
    String != BigInt
    ----------------
*/

bool operator!=(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) != rhs;
}


/*
    BigInt < String
    ---------------
*/

bool BigInt::operator<(const std::string& num) const {
    return *this < BigInt(num);
}


/*
    String < BigInt
    ---------------
*/

bool operator<(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) < rhs;
}


/*
    BigInt > String
    ---------------
*/

bool BigInt::operator>(const std::string& num) const {
    return *this > BigInt(num);
}


/*
    String > BigInt
    ---------------
*/

bool operator>(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) > rhs;
}


/*
    BigInt <= String
    ----------------
*/

bool BigInt::operator<=(const std::string& num) const {
    return !(*this > BigInt(num));
}


/*
    String <= BigInt
    ----------------
*/

bool operator<=(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) <= rhs;
}


/*
    BigInt >= String
    ----------------
*/

bool BigInt::operator>=(const std::string& num) const {
    return !(*this < BigInt(num));
}


/*
    String >= BigInt
    ----------------
*/

bool operator>=(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) >= rhs;
}

#endif  // BIG_INT_RELATIONAL_OPERATORS_HPP


/*
    ===========================================================================
    Math functions for BigInt
    ===========================================================================
*/

#ifndef BIG_INT_MATH_FUNCTIONS_HPP
#define BIG_INT_MATH_FUNCTIONS_HPP

#include <string>



/*
    abs
    ---
    Returns the absolute value of a BigInt.
*/

BigInt abs(const BigInt& num) {
    return num < 0 ? -num : num;
}


/*
    big_pow10
    ---------
    Returns a BigInt equal to 10^exp.
    NOTE: exponent should be a non-negative integer.
*/

BigInt big_pow10(size_t exp) {
    return BigInt("1" + std::string(exp, '0'));
}


/*
    pow (BigInt)
    ------------
    Returns a BigInt equal to base^exp.
*/

BigInt pow(const BigInt& base, int exp) {
    if (exp < 0) {
        if (base == 0)
            throw std::logic_error("Cannot divide by zero");
        return abs(base) == 1 ? base : 0;
    }
    if (exp == 0) {
        if (base == 0)
            throw std::logic_error("Zero cannot be raised to zero");
        return 1;
    }

    BigInt result = base, result_odd = 1;
    while (exp > 1) {
        if (exp % 2)
            result_odd *= result;
        result *= result;
        exp /= 2;
    }

    return result * result_odd;
}


/*
    pow (Integer)
    -------------
    Returns a BigInt equal to base^exp.
*/

BigInt pow(const long long& base, int exp) {
    return pow(BigInt(base), exp);
}


/*
    pow (String)
    ------------
    Returns a BigInt equal to base^exp.
*/

BigInt pow(const std::string& base, int exp) {
    return pow(BigInt(base), exp);

}


/*
    sqrt
    ----
    Returns the positive integer square root of a BigInt using Newton's method.
    NOTE: the input must be non-negative.
*/

BigInt sqrt(const BigInt& num) {
    if (num < 0)
        throw std::invalid_argument("Cannot compute square root of a negative integer");

    // Optimisations for small inputs:
    if (num == 0)
        return 0;
    else if (num < 4)
        return 1;
    else if (num < 9)
        return 2;
    else if (num < 16)
        return 3;

    BigInt sqrt_prev = 0;
    // The value for `sqrt_current` is chosen close to that of the actual
    // square root.
    // Since a number's square root has at least one less than half as many
    // digits as the number,
    //     sqrt_current = 10^(half_the_digits_in_num - 1)
    BigInt sqrt_current = big_pow10(num.to_string().size() / 2 - 1);

    while (abs(sqrt_current - sqrt_prev) > 1) {
        sqrt_prev = sqrt_current;
        sqrt_current = (num / sqrt_prev + sqrt_prev) / 2;
    }

    return sqrt_current;
}

#endif  // BIG_INT_MATH_FUNCTIONS_HPP


/*
    ===========================================================================
    Binary arithmetic operators
    ===========================================================================
*/

#ifndef BIG_INT_BINARY_ARITHMETIC_OPERATORS_HPP
#define BIG_INT_BINARY_ARITHMETIC_OPERATORS_HPP

#include <climits>
#include <cmath>
#include <string>


const long long FLOOR_SQRT_LLONG_MAX = 3037000499;


/*
    BigInt + BigInt
    ---------------
    The operand on the RHS of the addition is `num`.
*/

BigInt BigInt::operator+(const BigInt& num) const {
    // if the operands are of opposite signs, perform subtraction
    if (this->sign == '+' and num.sign == '-') {
        BigInt rhs = num;
        rhs.sign = '+';
        return *this - rhs;
    }
    else if (this->sign == '-' and num.sign == '+') {
        BigInt lhs = *this;
        lhs.sign = '+';
        return -(lhs - num);
    }

    // identify the numbers as `larger` and `smaller`
    std::string larger, smaller;
    std::tie(larger, smaller) = get_larger_and_smaller(this->value, num.value);

    BigInt result;      // the resultant sum
    result.value = "";  // the value is cleared as the digits will be appended
    short carry = 0, sum;
    // add the two values
    for (long i = larger.size() - 1; i >= 0; i--) {
        sum = larger[i] - '0' + smaller[i] - '0' + carry;
        result.value = std::to_string(sum % 10) + result.value;
        carry = sum / (short) 10;
    }
    if (carry)
        result.value = std::to_string(carry) + result.value;

    // if the operands are negative, the result is negative
    if (this->sign == '-' and result.value != "0")
        result.sign = '-';

    return result;
}


/*
    BigInt - BigInt
    ---------------
    The operand on the RHS of the subtraction is `num`.
*/

BigInt BigInt::operator-(const BigInt& num) const {
    // if the operands are of opposite signs, perform addition
    if (this->sign == '+' and num.sign == '-') {
        BigInt rhs = num;
        rhs.sign = '+';
        return *this + rhs;
    }
    else if (this->sign == '-' and num.sign == '+') {
        BigInt lhs = *this;
        lhs.sign = '+';
        return -(lhs + num);
    }

    BigInt result;      // the resultant difference
    // identify the numbers as `larger` and `smaller`
    std::string larger, smaller;
    if (abs(*this) > abs(num)) {
        larger = this->value;
        smaller = num.value;

        if (this->sign == '-')      // -larger - -smaller = -result
            result.sign = '-';
    }
    else {
        larger = num.value;
        smaller = this->value;

        if (num.sign == '+')        // smaller - larger = -result
            result.sign = '-';
    }
    // pad the smaller number with zeroes
    add_leading_zeroes(smaller, larger.size() - smaller.size());

    result.value = "";  // the value is cleared as the digits will be appended
    short difference;
    long i, j;
    // subtract the two values
    for (i = larger.size() - 1; i >= 0; i--) {
        difference = larger[i] - smaller[i];
        if (difference < 0) {
            for (j = i - 1; j >= 0; j--) {
                if (larger[j] != '0') {
                    larger[j]--;    // borrow from the j-th digit
                    break;
                }
            }
            j++;
            while (j != i) {
                larger[j] = '9';    // add the borrow and take away 1
                j++;
            }
            difference += 10;   // add the borrow
        }
        result.value = std::to_string(difference) + result.value;
    }
    strip_leading_zeroes(result.value);

    // if the result is 0, set its sign as +
    if (result.value == "0")
        result.sign = '+';

    return result;
}


/*
    BigInt * BigInt
    ---------------
    Computes the product of two BigInts using Karatsuba's algorithm.
    The operand on the RHS of the product is `num`.
*/

BigInt BigInt::operator*(const BigInt& num) const {
    if (*this == 0 or num == 0)
        return BigInt(0);
    if (*this == 1)
        return num;
    if (num == 1)
     return *this;

    BigInt product;
    if (abs(*this) <= FLOOR_SQRT_LLONG_MAX and abs(num) <= FLOOR_SQRT_LLONG_MAX)
        product = std::stoll(this->value) * std::stoll(num.value);
    else {
        // identify the numbers as `larger` and `smaller`
        std::string larger, smaller;
        std::tie(larger, smaller) = get_larger_and_smaller(this->value, num.value);

        size_t half_length = larger.size() / 2;
        auto half_length_ceil = (size_t) ceil(larger.size() / 2.0);

        BigInt num1_high, num1_low;
        num1_high = larger.substr(0, half_length);
        num1_low = larger.substr(half_length);

        BigInt num2_high, num2_low;
        num2_high = smaller.substr(0, half_length);
        num2_low = smaller.substr(half_length);

        strip_leading_zeroes(num1_high.value);
        strip_leading_zeroes(num1_low.value);
        strip_leading_zeroes(num2_high.value);
        strip_leading_zeroes(num2_low.value);

        BigInt prod_high, prod_mid, prod_low;
        prod_high = num1_high * num2_high;
        prod_low = num1_low * num2_low;
        prod_mid = (num1_high + num1_low) * (num2_high + num2_low)
                   - prod_high - prod_low;

        add_trailing_zeroes(prod_high.value, 2 * half_length_ceil);
        add_trailing_zeroes(prod_mid.value, half_length_ceil);

        strip_leading_zeroes(prod_high.value);
        strip_leading_zeroes(prod_mid.value);
        strip_leading_zeroes(prod_low.value);

        product = prod_high + prod_mid + prod_low;
    }
    strip_leading_zeroes(product.value);

    if (this->sign == num.sign)
        product.sign = '+';
    else
        product.sign = '-';

    return product;
}


/*
    divide
    ------
    Helper function that returns the quotient and remainder on dividing the
    dividend by the divisor, when the divisor is 1 to 10 times the dividend.
*/

std::tuple<BigInt, BigInt> divide(const BigInt& dividend, const BigInt& divisor) {
    BigInt quotient, remainder, temp;

    temp = divisor;
    quotient = 1;
    while (temp < dividend) {
        quotient++;
        temp += divisor;
    }
    if (temp > dividend) {
        quotient--;
        remainder = dividend - (temp - divisor);
    }

    return std::make_tuple(quotient, remainder);
}


/*
    BigInt / BigInt
    ---------------
    Computes the quotient of two BigInts using the long-division method.
    The operand on the RHS of the division (the divisor) is `num`.
*/

BigInt BigInt::operator/(const BigInt& num) const {
    BigInt abs_dividend = abs(*this);
    BigInt abs_divisor = abs(num);

    if (num == 0)
        throw std::logic_error("Attempted division by zero");
    if (abs_dividend < abs_divisor)
        return BigInt(0);
    if (num == 1)
        return *this;
    if (num == -1)
        return -(*this);

    BigInt quotient;
    if (abs_dividend <= LLONG_MAX and abs_divisor <= LLONG_MAX)
        quotient = std::stoll(abs_dividend.value) / std::stoll(abs_divisor.value);
    else if (abs_dividend == abs_divisor)
        quotient = 1;
    else {
        quotient.value = "";    // the value is cleared as digits will be appended
        BigInt chunk, chunk_quotient, chunk_remainder;
        size_t chunk_index = 0;
        chunk_remainder.value = abs_dividend.value.substr(chunk_index, abs_divisor.value.size() - 1);
        chunk_index = abs_divisor.value.size() - 1;
        while (chunk_index < abs_dividend.value.size()) {
            chunk.value = chunk_remainder.value.append(1, abs_dividend.value[chunk_index]);
            chunk_index++;
            while (chunk < abs_divisor) {
                quotient.value += "0";
                if (chunk_index < abs_dividend.value.size()) {
                    chunk.value.append(1, abs_dividend.value[chunk_index]);
                    chunk_index++;
                }
                else
                    break;
            }
            if (chunk == abs_divisor) {
                quotient.value += "1";
                chunk_remainder = 0;
            }
            else if (chunk > abs_divisor) {
                strip_leading_zeroes(chunk.value);
                std::tie(chunk_quotient, chunk_remainder) = divide(chunk, abs_divisor);
                quotient.value += chunk_quotient.value;
            }
        }
    }
    strip_leading_zeroes(quotient.value);

    if (this->sign == num.sign)
        quotient.sign = '+';
    else
        quotient.sign = '-';

    return quotient;
}


/*
    BigInt % BigInt
    ---------------
    Computes the modulo (remainder on division) of two BigInts.
    The operand on the RHS of the modulo (the divisor) is `num`.
*/

BigInt BigInt::operator%(const BigInt& num) const {
    BigInt abs_dividend = abs(*this);
    BigInt abs_divisor = abs(num);

    if (abs_divisor == 0)
        throw std::logic_error("Attempted division by zero");
    if (abs_divisor == 1 or abs_divisor == abs_dividend)
        return BigInt(0);

    BigInt remainder;
    if (abs_dividend <= LLONG_MAX and abs_divisor <= LLONG_MAX)
        remainder = std::stoll(abs_dividend.value) % std::stoll(abs_divisor.value);
    else if (abs_dividend < abs_divisor)
        remainder = abs_dividend;
    else {
        BigInt quotient = abs_dividend / abs_divisor;
        remainder = abs_dividend - quotient * abs_divisor;
    }
    strip_leading_zeroes(remainder.value);

    // remainder has the same sign as that of the dividend
    remainder.sign = this->sign;
    if (remainder.value == "0")     // except if its zero
        remainder.sign = '+';

    return remainder;
}


/*
    BigInt + Integer
    ----------------
*/

BigInt BigInt::operator+(const long long& num) const {
    return *this + BigInt(num);
}


/*
    Integer + BigInt
    ----------------
*/

BigInt operator+(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) + rhs;
}


/*
    BigInt - Integer
    ----------------
*/

BigInt BigInt::operator-(const long long& num) const {
    return *this - BigInt(num);
}


/*
    Integer - BigInt
    ----------------
*/

BigInt operator-(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) - rhs;
}


/*
    BigInt * Integer
    ----------------
*/

BigInt BigInt::operator*(const long long& num) const {
    return *this * BigInt(num);
}


/*
    Integer * BigInt
    ----------------
*/

BigInt operator*(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) * rhs;
}


/*
    BigInt / Integer
    ----------------
*/

BigInt BigInt::operator/(const long long& num) const {
    return *this / BigInt(num);
}


/*
    Integer / BigInt
    ----------------
*/

BigInt operator/(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) / rhs;
}


/*
    BigInt % Integer
    ----------------
*/

BigInt BigInt::operator%(const long long& num) const {
    return *this % BigInt(num);
}


/*
    Integer % BigInt
    ----------------
*/

BigInt operator%(const long long& lhs, const BigInt& rhs) {
    return BigInt(lhs) % rhs;
}


/*
    BigInt + String
    ---------------
*/

BigInt BigInt::operator+(const std::string& num) const {
    return *this + BigInt(num);
}


/*
    String + BigInt
    ---------------
*/

BigInt operator+(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) + rhs;
}


/*
    BigInt - String
    ---------------
*/

BigInt BigInt::operator-(const std::string& num) const {
    return *this - BigInt(num);
}


/*
    String - BigInt
    ---------------
*/

BigInt operator-(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) - rhs;
}


/*
    BigInt * String
    ---------------
*/

BigInt BigInt::operator*(const std::string& num) const {
    return *this * BigInt(num);
}


/*
    String * BigInt
    ---------------
*/

BigInt operator*(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) * rhs;
}


/*
    BigInt / String
    ---------------
*/

BigInt BigInt::operator/(const std::string& num) const {
    return *this / BigInt(num);
}


/*
    String / BigInt
    ---------------
*/

BigInt operator/(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) / rhs;
}


/*
    BigInt % String
    ---------------
*/

BigInt BigInt::operator%(const std::string& num) const {
    return *this % BigInt(num);
}


/*
    String % BigInt
    ---------------
*/

BigInt operator%(const std::string& lhs, const BigInt& rhs) {
    return BigInt(lhs) % rhs;
}

#endif  // BIG_INT_BINARY_ARITHMETIC_OPERATORS_HPP


/*
    ===========================================================================
    Arithmetic-assignment operators
    ===========================================================================
*/

#ifndef BIG_INT_ARITHMETIC_ASSIGNMENT_OPERATORS_HPP
#define BIG_INT_ARITHMETIC_ASSIGNMENT_OPERATORS_HPP



/*
    BigInt += BigInt
    ----------------
*/

BigInt& BigInt::operator+=(const BigInt& num) {
    *this = *this + num;

    return *this;
}


/*
    BigInt -= BigInt
    ----------------
*/

BigInt& BigInt::operator-=(const BigInt& num) {
    *this = *this - num;

    return *this;
}


/*
    BigInt *= BigInt
    ----------------
*/

BigInt& BigInt::operator*=(const BigInt& num) {
    *this = *this * num;

    return *this;
}


/*
    BigInt /= BigInt
    ----------------
*/

BigInt& BigInt::operator/=(const BigInt& num) {
    *this = *this / num;

    return *this;
}


/*
    BigInt %= BigInt
    ----------------
*/

BigInt& BigInt::operator%=(const BigInt& num) {
    *this = *this % num;

    return *this;
}


/*
    BigInt += Integer
    -----------------
*/

BigInt& BigInt::operator+=(const long long& num) {
    *this = *this + BigInt(num);

    return *this;
}


/*
    BigInt -= Integer
    -----------------
*/

BigInt& BigInt::operator-=(const long long& num) {
    *this = *this - BigInt(num);

    return *this;
}


/*
    BigInt *= Integer
    -----------------
*/

BigInt& BigInt::operator*=(const long long& num) {
    *this = *this * BigInt(num);

    return *this;
}


/*
    BigInt /= Integer
    -----------------
*/

BigInt& BigInt::operator/=(const long long& num) {
    *this = *this / BigInt(num);

    return *this;
}


/*
    BigInt %= Integer
    -----------------
*/

BigInt& BigInt::operator%=(const long long& num) {
    *this = *this % BigInt(num);

    return *this;
}


/*
    BigInt += String
    ----------------
*/

BigInt& BigInt::operator+=(const std::string& num) {
    *this = *this + BigInt(num);

    return *this;
}


/*
    BigInt -= String
    ----------------
*/

BigInt& BigInt::operator-=(const std::string& num) {
    *this = *this - BigInt(num);

    return *this;
}


/*
    BigInt *= String
    ----------------
*/

BigInt& BigInt::operator*=(const std::string& num) {
    *this = *this * BigInt(num);

    return *this;
}


/*
    BigInt /= String
    ----------------
*/

BigInt& BigInt::operator/=(const std::string& num) {
    *this = *this / BigInt(num);

    return *this;
}


/*
    BigInt %= String
    ----------------
*/

BigInt& BigInt::operator%=(const std::string& num) {
    *this = *this % BigInt(num);

    return *this;
}

#endif  // BIG_INT_ARITHMETIC_ASSIGNMENT_OPERATORS_HPP


/*
    ===========================================================================
    Increment and decrement operators
    ===========================================================================
*/

#ifndef BIG_INT_INCREMENT_DECREMENT_OPERATORS_HPP
#define BIG_INT_INCREMENT_DECREMENT_OPERATORS_HPP



/*
    Pre-increment
    -------------
    ++BigInt
*/

BigInt& BigInt::operator++() {
    *this += 1;

    return *this;
}


/*
    Pre-decrement
    -------------
    --BigInt
*/

BigInt& BigInt::operator--() {
    *this -= 1;

    return *this;
}


/*
    Post-increment
    --------------
    BigInt++
*/

BigInt BigInt::operator++(int) {
    BigInt temp = *this;
    *this += 1;

    return temp;
}


/*
    Post-decrement
    --------------
    BigInt--
*/

BigInt BigInt::operator--(int) {
    BigInt temp = *this;
    *this -= 1;

    return temp;
}

#endif  // BIG_INT_INCREMENT_DECREMENT_OPERATORS_HPP


/*
    ===========================================================================
    I/O stream operators
    ===========================================================================
*/

#ifndef BIG_INT_IO_STREAM_OPERATORS_HPP
#define BIG_INT_IO_STREAM_OPERATORS_HPP



/*
    BigInt from input stream
    ------------------------
*/

std::istream& operator>>(std::istream& in, BigInt& num) {
    std::string input;
    in >> input;
    num = BigInt(input);  // remove sign from value and set sign, if exists

    return in;
}


/*
    BigInt to output stream
    -----------------------
*/

std::ostream& operator<<(std::ostream& out, const BigInt& num) {
    if (num.sign == '-')
        out << num.sign;
    out << num.value;

    return out;
}

#endif  // BIG_INT_IO_STREAM_OPERATORS_HPP