From 87d14dce6fdab14ca4db15c510386f7a446c7dbb Mon Sep 17 00:00:00 2001
From: Shri Prakash Bajpai <68155959+Shri2206@users.noreply.github.com>
Date: Wed, 28 Oct 2020 19:38:10 +0530
Subject: [PATCH] Update modular_exponentiation.cpp

---
 math/modular_exponentiation.cpp | 112 ++++++++++++++++++--------------
 1 file changed, 64 insertions(+), 48 deletions(-)

diff --git a/math/modular_exponentiation.cpp b/math/modular_exponentiation.cpp
index 9c8dcf4cd..b85a9c874 100644
--- a/math/modular_exponentiation.cpp
+++ b/math/modular_exponentiation.cpp
@@ -1,7 +1,7 @@
 /**
  * @file
  * @brief C++ Program for Modular Exponentiation Iteratively.
- * Calculate the value of an integer a raised to an integer exponent b 
+ * @details The task is to calculate the value of an integer a raised to an integer exponent b 
  * under modulo c.
  * @note The time complexity of this approach is O(log b).
  *
@@ -13,67 +13,83 @@
  * 4 * 1
  * 4
  * We can also verify the result as 4^3 is 64 and 64 modulo 5 is 4
- */
-
+ *
+ * @author [Shri2206](https://github.com/Shri2206)
+*/
 #include <iostream> /// for io operations
+#include <cassert>  /// for assert
 
 /**
  * @namespace math
  * @brief Mathematical algorithms
  */
 namespace math {
-/**
-* @brief This function calculates a raised to exponent b 
-* under modulo c using modular exponentiation
-* @param a integer base
-* @param b unsigned integer exponent
-* @param c integer modulo
-* @return a raised to power b modulo c
-*/
-uint64_t power(uint64_t a, uint64_t b, uint64_t c)
-{ 
-	uint64_t ans = 1;	    	/// Initialize the answer to be returned 
-
-	a = a % c;          	/// Update a if it is more than or 
-				/// equal to c 
-
-	if (a == 0) 
-	{
-	    return 0;       	/// In case a is divisible by c; 
-	}
-
-	while (b > 0) 
+	
+	/**
+	* @brief This function calculates a raised to exponent b under modulo c using modular exponentiation.
+	* @param a integer base
+	* @param b unsigned integer exponent
+	* @param c integer modulo
+	* @return a raised to power b modulo c
+	*/
+	uint64_t power(uint64_t a, uint64_t b, uint64_t c)
 	{ 
-		/// If b is odd, multiply a with answer 
-		if (b & 1) 
+		uint64_t ans = 1;	    	/// Initialize the answer to be returned 
+		a = a % c;          		/// Update a if it is more than or equal to c  
+		if (a == 0) 
 		{
-			ans = (ans*a) % c; 
+		    return 0;       		/// In case a is divisible by c; 
 		}
-
-		/// b must be even now 
-		b = b>>1;       // b = b/2 
-		a = (a*a) % c; 
+		while (b > 0) 
+		{ 
+			/// If b is odd, multiply a with answer 
+			if (b & 1) 
+			{
+				ans = (ans*a) % c; 
+			}
+			/// b must be even now 
+			b = b>>1;       		/// b = b/2 
+			a = (a*a) % c; 
+		}
+		return ans; 
 	}
 
-	return ans; 
-}
 }  // namespace math 
 
 /**
-* @brief Main function
-* @returns 0 on exit
+ * Function for testing power function.
+ * test cases and assert statement.
+ * @returns `void`
 */
-int main() 
-{ 	
-	/// Give two numbers num1, num2 and modulo m
-	uint64_t num1 = 2; 
-	uint64_t num2 = 5; 
-	uint64_t m = 13; 
-
-	std::cout << "The value of "<<num1<<" raised to exponent "<<num2<< 
-	" under modulo "<<m<<" is " << math::power(num1, num2, m); 
-	/// std::cout << "The value of "<<num1<<" raised to exponent "<<num2<<" 
-	/// " under modulo "<<m<<" is " << power(num1, num2, m); 
-
-	return 0;
+static void test()
+{
+	int test_case_1 = math::power(2,5,13);
+	assert(test_case_1==6);
+	std::cout<<"Test 1 Passed!"<<std::endl;
+	
+	int test_case_2 = math::power(14,7,15);
+	assert(test_case_2==14);
+	std::cout<<"Test 2 Passed!"<<std::endl;
+	
+	int test_case_3 = math::power(8,15,41);
+	assert(test_case_3==32);
+	std::cout<<"Test 3 Passed!"<<std::endl;
+	
+	int test_case_4 = math::power(27,2,5);
+	assert(test_case_4==4);
+	std::cout<<"Test 4 Passed!"<<std::endl;
+	
+	int test_case_5 = math::power(7,3,6);
+	assert(test_case_5==1);
+	std::cout<<"Test 5 Passed!"<<std::endl;
 } 
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main() 
+{ 
+    test(); // execute the tests
+	return 0; 
+}