PollardRho.cpp

//  
//  algorithm - some algorithms in "Introduction to Algorithms", third edition
//  Copyright (C) 2018  lxylxy123456
//  
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU Affero General Public License as
//  published by the Free Software Foundation, either version 3 of the
//  License, or (at your option) any later version.
//  
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU Affero General Public License for more details.
//  
//  You should have received a copy of the GNU Affero General Public License
//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
//  

#ifndef MAIN
#define MAIN
#define MAIN_PollardRho
#endif

#ifndef FUNC_PollardRho
#define FUNC_PollardRho

#include "utils.h"

#include "Euclid.cpp"

template <typename T>
T abs(T x) {
	if (x < 0)
		return -x; 
	else
		return x; 
}

template <typename T>
T PollardRho(T n) {
	size_t i = 1, k = 2; 
    std::random_device rd; 
    std::uniform_int_distribution<T> dis(0, n - 1); 
	T x = dis(rd), y = x; 
	while (i < 1048576) {
		i++; 
		x = (x * x - 1) % n; 
		T d = Euclid(abs<T>(y - x), n); 
		if (d != 1 && d != n)
			return d; 
		if (i == k) {
			y = x; 
			k *= 2; 
		}
	}
	return 0; 
}
#endif

#ifdef MAIN_PollardRho
int main(int argc, char *argv[]) {
	const size_t nn = get_argv(argc, argv, 1, 30); 
	const size_t tries = get_argv(argc, argv, 2, 1); 
	using T = long long int; 
    std::random_device rd; 
    std::uniform_int_distribution<T> dis(1 << (nn - 1), 1 << nn); 
    for (size_t i = 0; i < tries; i++) {
		T n = get_argv(argc, argv, 3 + i, dis(rd) << 1 | 1); 
		std::cout << n << "\t" << std::flush << PollardRho(n) << std::endl;
	}
	return 0; 
}
#endif