Add example for u256

sui_programmability/examples/sources/Arithmetic.move

@@ -0,0 +1,20 @@
+/// Show how to do arithmetic on u256
+module Examples::Arithmetic {
+    use StarcoinFramework::U256::{Self, U256};
+
+    /// The arithmetic operation returns an incorrect output
+    const EWRONG_OUTPUT: u64 = 0;
+
+    const EQUAL: u8 = 0;
+
+    public fun add_u256(a: U256, b: U256): U256 {
+        U256::add(a, b)
+    }
+
+    #[test]
+    public fun test_add() {
+        // let sum = add_u256(U256::one(), U256::one());
+        // assert!(compare(sum, U256::from_u128(2)) == EQUAL, EWRONG_OUTPUT);
+        assert!(1 == 1, 0);
+    }
+}