Ho scritto qualcosa per questo recentemente per RSA in C++, un po 'disordinato però.
#include "BigInteger.h"
#include <iostream>
#include <sstream>
#include <stack>
BigInteger::BigInteger() {
digits.push_back(0);
negative = false;
}
BigInteger::~BigInteger() {
}
void BigInteger::addWithoutSign(BigInteger& c, const BigInteger& a, const BigInteger& b) {
int sum_n_carry = 0;
int n = (int)a.digits.size();
if (n < (int)b.digits.size()) {
n = b.digits.size();
}
c.digits.resize(n);
for (int i = 0; i < n; ++i) {
unsigned short a_digit = 0;
unsigned short b_digit = 0;
if (i < (int)a.digits.size()) {
a_digit = a.digits[i];
}
if (i < (int)b.digits.size()) {
b_digit = b.digits[i];
}
sum_n_carry += a_digit + b_digit;
c.digits[i] = (sum_n_carry & 0xFFFF);
sum_n_carry >>= 16;
}
if (sum_n_carry != 0) {
putCarryInfront(c, sum_n_carry);
}
while (c.digits.size() > 1 && c.digits.back() == 0) {
c.digits.pop_back();
}
//std::cout << a.toString() << " + " << b.toString() << " == " << c.toString() << std::endl;
}
void BigInteger::subWithoutSign(BigInteger& c, const BigInteger& a, const BigInteger& b) {
int sub_n_borrow = 0;
int n = a.digits.size();
if (n < (int)b.digits.size())
n = (int)b.digits.size();
c.digits.resize(n);
for (int i = 0; i < n; ++i) {
unsigned short a_digit = 0;
unsigned short b_digit = 0;
if (i < (int)a.digits.size())
a_digit = a.digits[i];
if (i < (int)b.digits.size())
b_digit = b.digits[i];
sub_n_borrow += a_digit - b_digit;
if (sub_n_borrow >= 0) {
c.digits[i] = sub_n_borrow;
sub_n_borrow = 0;
} else {
c.digits[i] = 0x10000 + sub_n_borrow;
sub_n_borrow = -1;
}
}
while (c.digits.size() > 1 && c.digits.back() == 0) {
c.digits.pop_back();
}
//std::cout << a.toString() << " - " << b.toString() << " == " << c.toString() << std::endl;
}
int BigInteger::cmpWithoutSign(const BigInteger& a, const BigInteger& b) {
int n = (int)a.digits.size();
if (n < (int)b.digits.size())
n = (int)b.digits.size();
//std::cout << "cmp(" << a.toString() << ", " << b.toString() << ") == ";
for (int i = n-1; i >= 0; --i) {
unsigned short a_digit = 0;
unsigned short b_digit = 0;
if (i < (int)a.digits.size())
a_digit = a.digits[i];
if (i < (int)b.digits.size())
b_digit = b.digits[i];
if (a_digit < b_digit) {
//std::cout << "-1" << std::endl;
return -1;
} else if (a_digit > b_digit) {
//std::cout << "+1" << std::endl;
return +1;
}
}
//std::cout << "0" << std::endl;
return 0;
}
void BigInteger::multByDigitWithoutSign(BigInteger& c, const BigInteger& a, unsigned short b) {
unsigned int mult_n_carry = 0;
c.digits.clear();
c.digits.resize(a.digits.size());
for (int i = 0; i < (int)a.digits.size(); ++i) {
unsigned short a_digit = 0;
unsigned short b_digit = b;
if (i < (int)a.digits.size())
a_digit = a.digits[i];
mult_n_carry += a_digit * b_digit;
c.digits[i] = (mult_n_carry & 0xFFFF);
mult_n_carry >>= 16;
}
if (mult_n_carry != 0) {
putCarryInfront(c, mult_n_carry);
}
//std::cout << a.toString() << " x " << b << " == " << c.toString() << std::endl;
}
void BigInteger::shiftLeftByBase(BigInteger& b, const BigInteger& a, int times) {
b.digits.resize(a.digits.size() + times);
for (int i = 0; i < times; ++i) {
b.digits[i] = 0;
}
for (int i = 0; i < (int)a.digits.size(); ++i) {
b.digits[i + times] = a.digits[i];
}
}
void BigInteger::shiftRight(BigInteger& a) {
//std::cout << "shr " << a.toString() << " == ";
for (int i = 0; i < (int)a.digits.size(); ++i) {
a.digits[i] >>= 1;
if (i+1 < (int)a.digits.size()) {
if ((a.digits[i+1] & 0x1) != 0) {
a.digits[i] |= 0x8000;
}
}
}
//std::cout << a.toString() << std::endl;
}
void BigInteger::shiftLeft(BigInteger& a) {
bool lastBit = false;
for (int i = 0; i < (int)a.digits.size(); ++i) {
bool bit = (a.digits[i] & 0x8000) != 0;
a.digits[i] <<= 1;
if (lastBit)
a.digits[i] |= 1;
lastBit = bit;
}
if (lastBit) {
a.digits.push_back(1);
}
}
void BigInteger::putCarryInfront(BigInteger& a, unsigned short carry) {
BigInteger b;
b.negative = a.negative;
b.digits.resize(a.digits.size() + 1);
b.digits[a.digits.size()] = carry;
for (int i = 0; i < (int)a.digits.size(); ++i) {
b.digits[i] = a.digits[i];
}
a.digits.swap(b.digits);
}
void BigInteger::divideWithoutSign(BigInteger& c, BigInteger& d, const BigInteger& a, const BigInteger& b) {
c.digits.clear();
c.digits.push_back(0);
BigInteger two("2");
BigInteger e = b;
BigInteger f("1");
BigInteger g = a;
BigInteger one("1");
while (cmpWithoutSign(g, e) >= 0) {
shiftLeft(e);
shiftLeft(f);
}
shiftRight(e);
shiftRight(f);
while (cmpWithoutSign(g, b) >= 0) {
g -= e;
c += f;
while (cmpWithoutSign(g, e) < 0) {
shiftRight(e);
shiftRight(f);
}
}
e = c;
e *= b;
f = a;
f -= e;
d = f;
}
BigInteger::BigInteger(const BigInteger& other) {
digits = other.digits;
negative = other.negative;
}
BigInteger::BigInteger(const char* other) {
digits.push_back(0);
negative = false;
BigInteger ten;
ten.digits[0] = 10;
const char* c = other;
bool make_negative = false;
if (*c == '-') {
make_negative = true;
++c;
}
while (*c != 0) {
BigInteger digit;
digit.digits[0] = *c - '0';
*this *= ten;
*this += digit;
++c;
}
negative = make_negative;
}
bool BigInteger::isOdd() const {
return (digits[0] & 0x1) != 0;
}
BigInteger& BigInteger::operator=(const BigInteger& other) {
if (this == &other) // handle self assignment
return *this;
digits = other.digits;
negative = other.negative;
return *this;
}
BigInteger& BigInteger::operator+=(const BigInteger& other) {
BigInteger result;
if (negative) {
if (other.negative) {
result.negative = true;
addWithoutSign(result, *this, other);
} else {
int a = cmpWithoutSign(*this, other);
if (a < 0) {
result.negative = false;
subWithoutSign(result, other, *this);
} else if (a > 0) {
result.negative = true;
subWithoutSign(result, *this, other);
} else {
result.negative = false;
result.digits.clear();
result.digits.push_back(0);
}
}
} else {
if (other.negative) {
int a = cmpWithoutSign(*this, other);
if (a < 0) {
result.negative = true;
subWithoutSign(result, other, *this);
} else if (a > 0) {
result.negative = false;
subWithoutSign(result, *this, other);
} else {
result.negative = false;
result.digits.clear();
result.digits.push_back(0);
}
} else {
result.negative = false;
addWithoutSign(result, *this, other);
}
}
negative = result.negative;
digits.swap(result.digits);
return *this;
}
BigInteger& BigInteger::operator-=(const BigInteger& other) {
BigInteger neg_other = other;
neg_other.negative = !neg_other.negative;
return *this += neg_other;
}
BigInteger& BigInteger::operator*=(const BigInteger& other) {
BigInteger result;
for (int i = 0; i < (int)digits.size(); ++i) {
BigInteger mult;
multByDigitWithoutSign(mult, other, digits[i]);
BigInteger shift;
shiftLeftByBase(shift, mult, i);
BigInteger add;
addWithoutSign(add, result, shift);
result = add;
}
if (negative != other.negative) {
result.negative = true;
} else {
result.negative = false;
}
//std::cout << toString() << " x " << other.toString() << " == " << result.toString() << std::endl;
negative = result.negative;
digits.swap(result.digits);
return *this;
}
BigInteger& BigInteger::operator/=(const BigInteger& other) {
BigInteger result, tmp;
divideWithoutSign(result, tmp, *this, other);
result.negative = (negative != other.negative);
negative = result.negative;
digits.swap(result.digits);
return *this;
}
BigInteger& BigInteger::operator%=(const BigInteger& other) {
BigInteger c, d;
divideWithoutSign(c, d, *this, other);
*this = d;
return *this;
}
bool BigInteger::operator>(const BigInteger& other) const {
if (negative) {
if (other.negative) {
return cmpWithoutSign(*this, other) < 0;
} else {
return false;
}
} else {
if (other.negative) {
return true;
} else {
return cmpWithoutSign(*this, other) > 0;
}
}
}
BigInteger& BigInteger::powAssignUnderMod(const BigInteger& exponent, const BigInteger& modulus) {
BigInteger zero("0");
BigInteger one("1");
BigInteger e = exponent;
BigInteger base = *this;
*this = one;
while (cmpWithoutSign(e, zero) != 0) {
//std::cout << e.toString() << " : " << toString() << " : " << base.toString() << std::endl;
if (e.isOdd()) {
*this *= base;
*this %= modulus;
}
shiftRight(e);
base *= BigInteger(base);
base %= modulus;
}
return *this;
}
std::string BigInteger::toString() const {
std::ostringstream os;
if (negative)
os << "-";
BigInteger tmp = *this;
BigInteger zero("0");
BigInteger ten("10");
tmp.negative = false;
std::stack<char> s;
while (cmpWithoutSign(tmp, zero) != 0) {
BigInteger tmp2, tmp3;
divideWithoutSign(tmp2, tmp3, tmp, ten);
s.push((char)(tmp3.digits[0] + '0'));
tmp = tmp2;
}
while (!s.empty()) {
os << s.top();
s.pop();
}
/*
for (int i = digits.size()-1; i >= 0; --i) {
os << digits[i];
if (i != 0) {
os << ",";
}
}
*/
return os.str();
E un esempio di utilizzo.
BigInteger a("87682374682734687"), b("435983748957348957349857345"), c("2348927349872344")
// Will Calculate pow(87682374682734687, 435983748957348957349857345) % 2348927349872344
a.powAssignUnderMod(b, c);
Anche veloce, e ha un numero illimitato di cifre.
grazie amico, quello ha fatto il trucco. Solo per curiosità, conosci qualche metodo che non richiederebbe l'uso di una memoria più grande? Sono sicuro che sarebbero tornati utili. –
Non che io sappia. Devi moltiplicare insieme due numeri fino a 673108, mod 673109. Ovviamente potresti rompere le cose e fare una lunga moltiplicazione con "cifre" più piccole, ad esempio 2^10. Ma non appena implementate la moltiplicazione e la divisione nel software, potreste anche implementarlo per il caso speciale di moltiplicare insieme due valori a 32 bit per ottenere un risultato a 64 bit, quindi dividendo per estrarre un resto a 32 bit. Potrebbero esserci alcune ottimizzazioni hard-core che fanno il minimo indispensabile, ma non le conosco e fingere un int a 64 bit in C++ non è * così * difficile. –