From e5967e6e7a95c9a67767d74853b618278f83b048 Mon Sep 17 00:00:00 2001
From: Zach S-B <zach@thesbfam.com>
Date: Fri, 5 Nov 2021 17:30:18 +1100
Subject: [PATCH] Bigint

---
 Q2Tools.java | 49 +++++++++++++++++++++++--------------------------
 1 file changed, 23 insertions(+), 26 deletions(-)

diff --git a/Q2Tools.java b/Q2Tools.java
index 17c54c0..de77b3a 100644
--- a/Q2Tools.java
+++ b/Q2Tools.java
@@ -26,36 +26,33 @@ public class Q2Tools {
      * @param B
      * @param C
      */
-    public void fastModularExpon(int A, int B, int C)
+    public BigInteger fastModularExpon(String base, String exponent, String modulus)
     {
-        String bInBinary = Integer.toBinaryString(B);
-
-        double test = 1;
+        // BigInteger baseVal = new BigInteger(base);
+        // BigInteger exponentVal = new BigInteger(exponent);
+        // BigInteger modulusVal = new BigInteger(modulus);  
         
-        {
-            int k = 0;
-            //Loop through the Binary String, starting from the right
-            for(int i = bInBinary.length()-1; i >= 0; i--)
-            {
-                
-                if(bInBinary.charAt(i)=='1')
-                {
-                    System.out.println("Loop: "+k);
-                    double step1 = Math.pow(2, k);
-                    System.out.println("STEP1: "+step1);
-
-                    double step2 = Math.pow(A, step1)%C;
-                    System.out.println("STEP2: "+step2);
-                    test= test*step2;
-
-                }
-                k++;
-            }
+        //modulusVal.equals(BigInteger.valueOf(1));
+        if(modulusVal == 1)
+        {  
+            return BigInteger.valueOf(0);
         }
 
-        
-        System.out.println(test);
+        BigInteger temp = new BigInteger("1");
 
-        System.out.println(Math.pow(5, 64)%19);
+        while(exponentVal>0)
+        {
+            if((exponentVal & 1)==1)
+            {
+               // temp = (temp * baseVal) % modulusVal;
+               temp = temp.multiply(BigInteger.valueOf(baseVal));
+               temp = temp.mod(BigInteger.valueOf(modulusVal));
+
+            }
+
+            exponentVal = exponentVal >> 1;
+            baseVal = (baseVal*baseVal) % modulusVal;
+        }
+        return temp;
     }
 }