ModularExponentiation.cpp

Author: lxylxy123456

ModLinEquationSolver.cpp

@@ -39,7 +39,6 @@ void ModularLinearEquationSolver(T a, T b, T n, std::vector<T>& ans) {
 			ans.push_back(((x0 + i * (n / d)) % n + n) % n); 
 	}
 }
-
 #endif
 
 #ifdef MAIN_ModLinEquationSolver

ModularExponentiation.cpp

@@ -0,0 +1,63 @@
+//  
+//  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_ModularExponentiation
+#endif
+
+#ifndef FUNC_ModularExponentiation
+#define FUNC_ModularExponentiation
+
+#include "utils.h"
+
+#include "Euclid.cpp"
+
+template <typename T>
+T ModularExponentiation(T a, T b, T n) {
+	T c = 0; 
+	T d = 1; 
+	for (T i = log2(b); i >= 0; i--) {
+		c *= 2; 
+		d = d * d % n; 
+		if (b & 1 << i) {
+			c++; 
+			d = d * a % n; 
+		}
+	}
+	assert(c == b); 
+	return d; 
+}
+#endif
+
+#ifdef MAIN_ModularExponentiation
+int main(int argc, char *argv[]) {
+	const size_t nn = get_argv(argc, argv, 1, 4); 
+	using T = long long int; 
+    std::random_device rd; 
+    std::uniform_int_distribution<T> dis(0, 1 << nn); 
+    std::uniform_int_distribution<T> disn(1, 1 << nn); 
+	T a = get_argv(argc, argv, 2, dis(rd)); 
+	T b = get_argv(argc, argv, 3, dis(rd)); 
+	T n = get_argv(argc, argv, 4, disn(rd)); 
+	T ans = ModularExponentiation(a, b, n); 
+	std::cout << a << " ** " << b << " % " << n << " = " << ans << std::endl; 
+	return 0; 
+}
+#endif
+

README.md

@@ -200,6 +200,7 @@
 | 31 | Euclid.cpp					| Euclid								|  935 |
 | 31 | Euclid.cpp					| Extended Euclid						|  937 |
 | 31 | ModLinEquationSolver.cpp		| Modular Linear Equation Solver		|  949 |
+| 31 | ModularExponentiation.cpp	| Modular Exponentiation				|  957 |
 
 # Supplementary Files
 * `utils.h`: Utils