From 926c1a9b39ac5d68d74103f3d106c1371b4c5e6e Mon Sep 17 00:00:00 2001
From: Zach S-B <zach@thesbfam.com>
Date: Fri, 5 Nov 2021 18:02:46 +1100
Subject: [PATCH] working fme

---
 Q2.java      |  2 +-
 Q2Tools.java | 44 ++++++++++++++++++++++----------------------
 2 files changed, 23 insertions(+), 23 deletions(-)

diff --git a/Q2.java b/Q2.java
index 2c15008..d25dbaf 100644
--- a/Q2.java
+++ b/Q2.java
@@ -33,7 +33,7 @@ public static void main(String[] args)
 
     Q2Tools toolbox = new Q2Tools();
 
-    toolbox.fastModularExpon(5, 117, 19);
+    System.out.println(toolbox.fastModularExpon("3785", "8395", "65537"));
 }
 
 }
\ No newline at end of file
diff --git a/Q2Tools.java b/Q2Tools.java
index de77b3a..b813c95 100644
--- a/Q2Tools.java
+++ b/Q2Tools.java
@@ -20,39 +20,39 @@ public class Q2Tools {
 
     }
 
-    /**
-     * A^B mod C
-     * @param A
-     * @param B
-     * @param C
-     */
-    public BigInteger fastModularExpon(String base, String exponent, String modulus)
+/**
+ * Performs a fast modular exponation, (base^exponent)%modulus.
+ * Takes input values as strings containg the numbers
+ * @param base
+ * @param exponent
+ * @param modulus
+ * @return
+ */
+    public BigInteger fme(String base, String exponent, String modulus)
     {
-        // BigInteger baseVal = new BigInteger(base);
-        // BigInteger exponentVal = new BigInteger(exponent);
-        // BigInteger modulusVal = new BigInteger(modulus);  
+        BigInteger baseVal = new BigInteger(base);
+        BigInteger exponentVal = new BigInteger(exponent);
+        BigInteger modulusVal = new BigInteger(modulus);  
         
-        //modulusVal.equals(BigInteger.valueOf(1));
-        if(modulusVal == 1)
+        if(modulusVal.equals(BigInteger.valueOf(1)))
         {  
             return BigInteger.valueOf(0);
         }
 
-        BigInteger temp = new BigInteger("1");
+        BigInteger result = new BigInteger("1");
 
-        while(exponentVal>0)
-        {
-            if((exponentVal & 1)==1)
+        while(exponentVal.compareTo(BigInteger.valueOf(0))==1)
+        {   
+            if(exponentVal.and(BigInteger.valueOf(1)).compareTo(BigInteger.valueOf(1))==0)
             {
-               // temp = (temp * baseVal) % modulusVal;
-               temp = temp.multiply(BigInteger.valueOf(baseVal));
-               temp = temp.mod(BigInteger.valueOf(modulusVal));
+               result = result.multiply(baseVal);
+               result = result.mod(modulusVal);
 
             }
 
-            exponentVal = exponentVal >> 1;
-            baseVal = (baseVal*baseVal) % modulusVal;
+            exponentVal = exponentVal.shiftRight(1);
+            baseVal = (baseVal.multiply(baseVal)).mod(modulusVal);
         }
-        return temp;
+        return result;
     }
 }