New account_db key scheme; snapshot tests

ethcore/src/account_db.rs

@@ -13,7 +13,10 @@ pub struct AccountDB<'db> {
 
 #[inline]
 fn combine_key<'a>(address: &'a H256, key: &'a H256) -> H256 {
-	address ^ key
+	let mut addr_hash = address.sha3();
+	// preserve 96 bits of original key for db lookup
+	addr_hash[0..12].clone_from_slice(&[0u8; 12]); 
+	&addr_hash ^ key
 }
 
 impl<'db> AccountDB<'db> {

ethcore/src/state.rs

@@ -482,6 +482,38 @@ fn ensure_cached() {
 	assert_eq!(state.root().hex(), "0ce23f3c809de377b008a4a3ee94a0834aac8bec1f86e28ffe4fdb5a15b0c785");
 }
 
+#[test]
+fn snapshot_basic() {
+	let mut state_result = get_temp_state();
+	let mut state = state_result.reference_mut();
+	let a = Address::zero();
+	state.snapshot();
+	state.add_balance(&a, &U256::from(69u64));
+	assert_eq!(state.balance(&a), U256::from(69u64));
+	state.clear_snapshot();
+	assert_eq!(state.balance(&a), U256::from(69u64));
+	state.snapshot();
+	state.add_balance(&a, &U256::from(1u64));
+	assert_eq!(state.balance(&a), U256::from(70u64));
+	state.revert_snapshot();
+	assert_eq!(state.balance(&a), U256::from(69u64));
+}
+
+#[test]
+fn snapshot_nested() {
+	let mut state_result = get_temp_state();
+	let mut state = state_result.reference_mut();
+	let a = Address::zero();
+	state.snapshot();
+	state.snapshot();
+	state.add_balance(&a, &U256::from(69u64));
+	assert_eq!(state.balance(&a), U256::from(69u64));
+	state.clear_snapshot();
+	assert_eq!(state.balance(&a), U256::from(69u64));
+	state.revert_snapshot();
+	assert_eq!(state.balance(&a), U256::from(0));
+}
+
 #[test]
 fn create_empty() {
 	let mut state_result = get_temp_state();