addition base case to tenscolumns

src/addition.c

@@ -13,5 +13,5 @@ unsigned int addition(unsigned int a, unsigned int b) {
 
     full_adder(s, nc, a, b, 0);
 
-    return (unsigned int) s[0];
+    return (unsigned int) s[0] ^ (nc[0] << 1);
 }