From 115ed2efbf0d97140bfbdd96f2e583835868e8d9 Mon Sep 17 00:00:00 2001
From: Sebastian Hugentobler <sebastian@vanwa.ch>
Date: Thu, 17 Mar 2022 17:59:32 +0100
Subject: [PATCH] implement bit swapping

---
 src/main/java/ch/fhnw/kry/SPN.java     | 17 ++++-------------
 src/test/java/ch/fhnw/kry/SPNTest.java |  6 ++++--
 2 files changed, 8 insertions(+), 15 deletions(-)

diff --git a/src/main/java/ch/fhnw/kry/SPN.java b/src/main/java/ch/fhnw/kry/SPN.java
index b17ea73..cbcbfd2 100644
--- a/src/main/java/ch/fhnw/kry/SPN.java
+++ b/src/main/java/ch/fhnw/kry/SPN.java
@@ -62,20 +62,11 @@ public class SPN {
     }
 
     public int swapBits(int x, int a, int b) {
-        int tmpA = (x & (0x1 << (15 - a)));
-        int tmpB = (x & (0x1 << (15 - b)));
-        
-        tmpA = tmpA == 0 ? 0 : 1;
-        tmpB = tmpB == 0 ? 0 : 1;
+        a = 15 - a;
+        b = 15 - b;
 
-        tmpA = tmpA << (15 -b);
-        tmpB = tmpB << (15 - a);
-
-        x = x | tmpA;
-        x = x | tmpB;
-
-        // x = tmpA == 0 ? (x & 0x1 << 15 - b) | 0b0 : (x & 0x1 << 15 - b) | ~0b0;
-        // x = tmpB == 0 ? (x & 0x1 << 15 - a) | 0b0 : (x & 0x1 << 15 - a) | ~0b0;
+        x ^= (1 << a);
+        x ^= (1 << b);
 
         return x;
     }
diff --git a/src/test/java/ch/fhnw/kry/SPNTest.java b/src/test/java/ch/fhnw/kry/SPNTest.java
index 63952b1..83dd4eb 100644
--- a/src/test/java/ch/fhnw/kry/SPNTest.java
+++ b/src/test/java/ch/fhnw/kry/SPNTest.java
@@ -43,11 +43,13 @@ class SPNTest {
         int r = 0xC;
 
         // when
-        int y = spn.swapBits(x, 1, 2);
-        int yy = spn.swapBits(x, 2, 1);
+        int y = spn.swapBits(x, 13, 14);
+        int yy = spn.swapBits(x, 14, 13);
+        int yyy = spn.swapBits(x, 14, 14);
 
         // then
         assertEquals(r, y);
         assertEquals(r, yy);
+        assertEquals(x, yyy);
     }
 }