308 lines
8.4 KiB
C++
308 lines
8.4 KiB
C++
#include <cmath>
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#include <cstdint>
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#include <iostream>
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#include <numeric>
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#include <stdexcept>
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#include <string>
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#include <vector>
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class Rational {
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public:
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Rational(const int32_t& aNumerator, const int32_t& aDenominator) {
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if ( aDenominator < 0 ) {
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numerator = -aNumerator;
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denominator = -aDenominator;
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} else {
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numerator = aNumerator;
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denominator = aDenominator;
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}
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if ( aNumerator == 0 ) {
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denominator = 1;
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}
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const uint32_t divisor = std::gcd(numerator, denominator);
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numerator /= divisor;
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denominator /= divisor;
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}
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std::string to_string() const {
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return std::to_string(numerator) + " / " + std::to_string(denominator);
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}
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private:
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int32_t numerator;
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int32_t denominator;
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};
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class P_adic {
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public:
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// Create a P_adic number, with p = 'prime', from the given rational 'numerator' / 'denominator'.
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P_adic(const uint32_t& prime, int32_t numerator, int32_t denominator) : prime(prime) {
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if ( denominator == 0 ) {
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throw std::invalid_argument("Denominator cannot be zero");
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}
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order = 0;
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// Process rational zero
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if ( numerator == 0 ) {
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digits.assign(DIGITS_SIZE, 0);
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order = ORDER_MAX;
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return;
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}
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// Remove multiples of 'prime' and adjust the order of the P_adic number accordingly
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while ( modulo_prime(numerator) == 0 ) {
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numerator /= static_cast<int32_t>(prime);
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order += 1;
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}
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while ( modulo_prime(denominator) == 0 ) {
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denominator /= static_cast<int32_t>(prime);
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order -= 1;
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}
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// Standard calculation of P_adic digits
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const uint64_t inverse = modulo_inverse(denominator);
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while ( digits.size() < DIGITS_SIZE ) {
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const uint32_t digit = modulo_prime(numerator * inverse);
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digits.emplace_back(digit);
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numerator -= digit * denominator;
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if ( numerator != 0 ) {
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// The denominator is not a power of a prime
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uint32_t count = 0;
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while ( modulo_prime(numerator) == 0 ) {
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numerator /= static_cast<int32_t>(prime);
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count += 1;
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}
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for ( uint32_t i = count; i > 1; --i ) {
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digits.emplace_back(0);
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}
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}
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}
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}
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// Return the sum of this P_adic number with the given P_adic number.
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P_adic add(P_adic other) {
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if ( prime != other.prime ) {
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throw std::invalid_argument("Cannot add p-adic's with different primes");
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}
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std::vector<uint32_t> this_digits = digits;
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std::vector<uint32_t> other_digits = other.digits;
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std::vector<uint32_t> result;
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// Adjust the digits so that the P_adic points are aligned
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for ( int32_t i = 0; i < -order + other.order; ++i ) {
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other_digits.insert(other_digits.begin(), 0);
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}
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for ( int32_t i = 0; i < -other.order + order; ++i ) {
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this_digits.insert(this_digits.begin(), 0);
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}
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// Standard digit by digit addition
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uint32_t carry = 0;
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for ( uint32_t i = 0; i < std::min(this_digits.size(), other_digits.size()); ++i ) {
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const uint32_t sum = this_digits[i] + other_digits[i] + carry;
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const uint32_t remainder = sum % prime;
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carry = ( sum >= prime ) ? 1 : 0;
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result.emplace_back(remainder);
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}
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return P_adic(prime, result, all_zero_digits(result) ? ORDER_MAX : std::min(order, other.order));
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}
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// Return the Rational representation of this P_adic number.
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Rational convert_to_rational() {
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std::vector<uint32_t> numbers = digits;
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// Zero
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if ( numbers.empty() || all_zero_digits(numbers) ) {
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return Rational(1, 0);
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}
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// Positive integer
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if ( order >= 0 && ends_with(numbers, 0) ) {
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for ( int32_t i = 0; i < order; ++i ) {
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numbers.emplace(numbers.begin(), 0);
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}
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return Rational(convert_to_decimal(numbers), 1);
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}
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// Negative integer
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if ( order >= 0 && ends_with(numbers, prime - 1) ) {
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negate_digits(numbers);
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for ( int32_t i = 0; i < order; ++i ) {
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numbers.emplace(numbers.begin(), 0);
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}
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return Rational(-convert_to_decimal(numbers), 1);
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}
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// Rational
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const P_adic copy(prime, digits, order);
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P_adic sum(prime, digits, order);
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int32_t denominator = 1;
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do {
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sum = sum.add(copy);
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denominator += 1;
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} while ( ! ( ends_with(sum.digits, 0) || ends_with(sum.digits, prime - 1) ) );
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const bool negative = ends_with(sum.digits, 6);
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if ( negative ) {
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negate_digits(sum.digits);
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}
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int32_t numerator = negative ? -convert_to_decimal(sum.digits) : convert_to_decimal(sum.digits);
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if ( order > 0 ) {
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numerator *= std::pow(prime, order);
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}
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if ( order < 0 ) {
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denominator *= std::pow(prime, -order);
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}
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return Rational(numerator, denominator);
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}
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// Return a string representation of this P_adic number.
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std::string to_string() {
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std::vector<uint32_t> numbers = digits;
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pad_with_zeros(numbers);
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std::string result = "";
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for ( int64_t i = numbers.size() - 1; i >= 0; --i ) {
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result += std::to_string(digits[i]);
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}
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if ( order >= 0 ) {
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for ( int32_t i = 0; i < order; ++i ) {
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result += "0";
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}
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result += ".0";
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} else {
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result.insert(result.length() + order, ".");
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while ( result[result.length() - 1] == '0' ) {
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result = result.substr(0, result.length() - 1);
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}
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}
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return " ..." + result.substr(result.length() - PRECISION - 1);
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}
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private:
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/**
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* Create a P_adic, with p = 'prime', directly from a vector of digits.
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*
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* For example: with 'order' = 0, the vector [1, 2, 3, 4, 5] creates the p-adic ...54321.0,
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* 'order' > 0 shifts the vector 'order' places to the left and
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* 'order' < 0 shifts the vector 'order' places to the right.
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*/
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P_adic(const uint32_t& prime, const std::vector<uint32_t>& digits, const int32_t& order)
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: prime(prime), digits(digits), order(order) {
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}
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// Transform the given vector of digits representing a P_adic number
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// into a vector which represents the negation of the P_adic number.
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void negate_digits(std::vector<uint32_t>& numbers) {
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numbers[0] = modulo_prime(prime - numbers[0]);
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for ( uint64_t i = 1; i < numbers.size(); ++i ) {
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numbers[i] = prime - 1 - numbers[i];
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}
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}
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// Return the multiplicative inverse of the given number modulo 'prime'.
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uint32_t modulo_inverse(const uint32_t& number) const {
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uint32_t inverse = 1;
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while ( modulo_prime(inverse * number) != 1 ) {
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inverse += 1;
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}
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return inverse;
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}
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// Return the given number modulo 'prime' in the range 0..'prime' - 1.
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int32_t modulo_prime(const int64_t& number) const {
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const int32_t div = static_cast<int32_t>(number % prime);
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return ( div >= 0 ) ? div : div + prime;
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}
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// The given vector is padded on the right by zeros up to a maximum length of 'DIGITS_SIZE'.
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void pad_with_zeros(std::vector<uint32_t>& vector) {
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while ( vector.size() < DIGITS_SIZE ) {
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vector.emplace_back(0);
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}
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}
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// Return the given vector of base 'prime' integers converted to a decimal integer.
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uint32_t convert_to_decimal(const std::vector<uint32_t>& numbers) const {
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uint32_t decimal = 0;
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uint32_t multiple = 1;
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for ( const uint32_t& number : numbers ) {
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decimal += number * multiple;
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multiple *= prime;
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}
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return decimal;
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}
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// Return whether the given vector consists of all zeros.
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bool all_zero_digits(const std::vector<uint32_t>& numbers) const {
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for ( uint32_t number : numbers ) {
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if ( number != 0 ) {
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return false;
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}
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}
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return true;
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}
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// Return whether the given vector ends with multiple instances of the given number.
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bool ends_with(const std::vector<uint32_t>& numbers, const uint32_t& number) const {
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for ( uint64_t i = numbers.size() - 1; i >= numbers.size() - PRECISION / 2; --i ) {
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if ( numbers[i] != number ) {
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return false;
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}
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}
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return true;
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}
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uint32_t prime;
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std::vector<uint32_t> digits;
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int32_t order;
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static const uint32_t PRECISION = 40;
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static const uint32_t ORDER_MAX = 1'000;
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static const uint32_t DIGITS_SIZE = PRECISION + 5;
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};
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int main() {
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std::cout << "3-adic numbers:" << std::endl;
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P_adic padic_one(3, -2, 87);
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std::cout << "-2 / 87 => " << padic_one.to_string() << std::endl;
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P_adic padic_two(3, 4, 97);
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std::cout << "4 / 97 => " << padic_two.to_string() << std::endl;
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P_adic sum = padic_one.add(padic_two);
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std::cout << "sum => " << sum.to_string() << std::endl;
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std::cout << "Rational = " << sum.convert_to_rational().to_string() << std::endl;
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std::cout << std::endl;
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std::cout << "7-adic numbers:" << std::endl;
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padic_one = P_adic(7, 5, 8);
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std::cout << "5 / 8 => " << padic_one.to_string() << std::endl;
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padic_two = P_adic(7, 353, 30809);
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std::cout << "353 / 30809 => " << padic_two.to_string() << std::endl;
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sum = padic_one.add(padic_two);
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std::cout << "sum => " << sum.to_string() << std::endl;
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std::cout << "Rational = " << sum.convert_to_rational().to_string() << std::endl;
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std::cout << std::endl;
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}
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