taming-cpp

bigint.h (5989B)

---

 // Taken from https://git.tronto.net/zmodn
 
 #ifndef BIGUNSIGNED_H
 #define BIGUNSIGNED_H
 
 #include <cstdint>
 #include <iostream>
 #include <string_view>
 
 constexpr uint64_t abs64(int64_t);
 constexpr uint64_t pow10(uint64_t);
 
 // Big integer class for numbers of at most N decimal digits.
 // The number E is used to tune the size of each digit, mostly for
 // testing purposes.
 
 template<uint64_t N = 50, uint64_t E = 9>
 requires (E < 10)
 class BigInt {
 public:
 	// The member variables sign and digits are declared public so that
 	// BigInt becomes a structural type and can be used in templates.
 
 	static constexpr uint64_t M = pow10(E);
 	static constexpr uint64_t D = (N / E) + 1;
 
 	bool sign;
 	uint64_t digits[D];
 
 	constexpr BigInt() : sign{true} {
 		std::fill(digits, digits+D, 0);
 	}
 
 	constexpr BigInt(int64_t n) : sign{n >= 0} {
 		std::fill(digits, digits+D, 0);
 		digits[0] = abs64(n);
 		carryover();
 	}
 
 	constexpr BigInt(const std::string_view s) : sign{true} {
 		std::fill(digits, digits+D, 0);
 		if (s.size() == 0)
 			return;
 		for (int i = s.size()-1, j = 0; i >= 0; i--, j++) {
 			if (s[i] == '\'')
 				continue;
 			if (i == 0 && s[i] == '-') {
 				sign = false;
 				break;
 			}
 			digits[j/E] += (pow10(j % E))
 			    * static_cast<uint64_t>(s[i] - '0');
 		}
 	}
 
 	constexpr auto operator<=>(const BigInt& other) const {
 		if (sign != other.sign)
 			return sign <=> other.sign;
 
 		for (int i = D-1; i >= 0; i--)
 			if (digits[i] != other.digits[i])
 				return sign ?
 				    digits[i] <=> other.digits[i] :
 				    other.digits[i] <=> digits[i];
 
 		return 0 <=> 0;
 	}
 
 	constexpr bool operator==(const BigInt& other) const = default;
 
 	constexpr BigInt abs() const {
 		BigInt ret = *this;
 		ret.sign = true;
 		return ret;
 	}
 
 	constexpr BigInt operator-() const {
 		if (*this == 0)
 			return 0;
 		BigInt ret = *this;
 		ret.sign = !ret.sign;
 		return ret;
 	}
 
 	constexpr BigInt operator+(const BigInt& z) const {
 		if (sign && z.sign)
 			return positive_sum(*this, z);
 		else if (sign && !z.sign)
 			return positive_diff(*this, -z);
 		else if (!sign && z.sign)
 			return positive_diff(z, -*this);
 		else
 			return -positive_sum(-*this, -z);
 	}
 
 	constexpr BigInt operator-(const BigInt& z) const {
 		return *this + (-z);
 	}
 
 	constexpr BigInt operator*(const BigInt& z) const {
 		BigInt ret;
 		ret.sign = !(sign ^ z.sign);
 		for (int i = 0; i < D; i++)
 			for (int j = 0; i+j < D; j++)
 				ret.digits[i+j] += digits[i] * z.digits[j];
 		ret.carryover();
 		return ret;
 	}
 
 	constexpr BigInt operator/(const BigInt& z) const {
 		auto [q, r] = euclidean_division(*this, z);
 		return q;
 	}
 
 	constexpr BigInt operator%(const BigInt& z) const {
 		auto [q, r] = euclidean_division(*this, z);
 		return r;
 	}
 
 	constexpr BigInt operator+=(const BigInt& z) { return *this = *this + z; }
 	constexpr BigInt operator++() { return *this += 1; }
 	constexpr BigInt operator-=(const BigInt& z) { return *this = *this - z; }
 	constexpr BigInt operator--() { return *this -= 1; }
 	constexpr BigInt operator*=(const BigInt& z) { return *this = *this * z; }
 	constexpr BigInt operator/=(const BigInt& z) { return *this = *this / z; }
 	constexpr BigInt operator%=(const BigInt& z) { return *this = *this % z; }
 
 	friend std::ostream& operator<<(std::ostream& os, const BigInt<N, E>& z) {
 		if (z == 0) {
 			os << "0";
 			return os;
 		}
 
 		if (!z.sign)
 			os << "-";
 
 		int j;
 		for (j = z.D-1; z.digits[j] == 0; j--) ;
 		os << z.digits[j]; // Top digit is not padded
 
 		for (int i = j-1; i >= 0; i--) {
 			std::string num = std::to_string(z.digits[i]);
 			os << std::string(E - num.length(), '0') << num;
 		}
 		return os;
 	}
 
 private:
 	constexpr void carryover() {
 		for (int i = 1; i < D; i++) {
 			auto c = digits[i-1] / M;
 			digits[i-1] -= c * M;
 			digits[i] += c;
 		}
 	}
 
 	constexpr BigInt half() const {
 		BigInt ret;
 		uint64_t carry = 0;
 		for (int i = D-1; i >= 0; i--) {
 			ret.digits[i] += (digits[i] + M * carry) / 2;
 			carry = digits[i] % 2;
 		}
 		return ret;
 	}
 
 	static constexpr BigInt powM(uint64_t e) {
 		BigInt ret;
 		ret.digits[e] = 1;
 		return ret;
 	}
 
 	// Sum of non-negative integers
 	static constexpr BigInt positive_sum(const BigInt& x, const BigInt& y) {
 		BigInt ret;
 		for (int i = 0; i < D; i++)
 			ret.digits[i] = x.digits[i] + y.digits[i];
 		ret.carryover();
 		return ret;
 	}
 
 	// Difference of non-negative integers (result may be negative)
 	static constexpr BigInt positive_diff(const BigInt& x, const BigInt& y) {
 		if (y > x)
 			return -positive_diff(y, x);
 
 		BigInt ret;
 		uint64_t carry = 0;
 		for (int i = 0; i < D; i++) {
 			uint64_t oldcarry = carry;
 			if (x.digits[i] < y.digits[i] + oldcarry) {
 				ret.digits[i] = M;
 				carry = 1;
 			} else {
 				carry = 0;
 			}
 			ret.digits[i] += x.digits[i];
 			ret.digits[i] -= y.digits[i] + oldcarry;
 		}
 		ret.carryover();
 		return ret;
 	}
 
 	// Division with remainder, UB if y == 0
 	static constexpr std::pair<BigInt, BigInt>
 	euclidean_division(const BigInt& x, const BigInt& y) {
 		auto [q, r] = positive_div(x.abs(), y.abs());
 		if (x.sign && y.sign)
 			return std::pair(q, r);
 		else if (x.sign && !y.sign)
 			return r == 0 ? std::pair(-q, 0) : std::pair(-q-1, y+r);
 		else if (!x.sign && y.sign)
 			return r == 0 ? std::pair(-q, r) : std::pair(-q-1, y-r);
 		else
 			return std::pair(q, -r);
 	}
 
 	// Division with remainder of non-negative integers, UB if y == 0
 	// This method is inefficient (O(log(x/y)) BigInt multiplications)
 	static constexpr std::pair<BigInt, BigInt>
 	positive_div(const BigInt& x, const BigInt& y) {
 		BigInt q = 0;
 		BigInt r = x;
 
 		if (y > x)
 			return std::pair(q, r);
 
 		BigInt lb = 0;
 		BigInt ub = x;
 		while (true) {
 			BigInt q = (ub + lb).half();
 			BigInt r = x - y*q;
 
 			if (r < 0)
 				ub = q;
 			else if (r >= y)
 				lb = q+1;
 			else
 				return std::pair(q, r);
 		}
 	}
 };
 
 constexpr uint64_t abs64(int64_t x) {
 	return static_cast<uint64_t>(x > 0 ? x : -x);
 }
 
 constexpr uint64_t pow10(uint64_t e) {
 	if (e == 0)
 		return 1;
 	else
 		return 10 * pow10(e-1);
 }
 
 #endif