adjust storage update evm-style (#7812)

ethcore/res/wasm-tests

@@ -1 +1 @@
-Subproject commit ff8504a7f3b3fe78af47fa4e0c24e4a75a7306fd
+Subproject commit fb111c82deff8759f54a5038d07cecc77cb5a663

ethcore/wasm/src/runtime.rs

@@ -218,11 +218,21 @@ impl<'a> Runtime<'a> {
 		let key = self.h256_at(args.nth(0)?)?;
 		let val_ptr: u32 = args.nth(1)?;
 
-		self.adjusted_charge(|schedule| schedule.sstore_set_gas as u64)?;
-
 		let val = self.h256_at(val_ptr)?;
+		let former_val = self.ext.storage_at(&key).map_err(|_| Error::StorageUpdateError)?;
+
+		if former_val == H256::zero() && val != H256::zero() {
+			self.adjusted_charge(|schedule| schedule.sstore_set_gas as u64)?;
+		} else {
+			self.adjusted_charge(|schedule| schedule.sstore_reset_gas as u64)?;
+		}
+
 		self.ext.set_storage(key, val).map_err(|_| Error::StorageUpdateError)?;
 
+		if former_val != H256::zero() && val == H256::zero() {
+			self.ext.inc_sstore_clears();
+		}
+
 		Ok(())
 	}
 

ethcore/wasm/src/tests.rs

@@ -659,6 +659,53 @@ fn math_div() {
 	assert_eq!(gas_left, U256::from(90_607));
 }
 
+#[test]
+fn storage_metering() {
+	::ethcore_logger::init_log();
+
+	// #1
+	let mut ext = FakeExt::new();
+
+	let code = Arc::new(load_sample!("setter.wasm"));
+	let address: Address = "0f572e5295c57f15886f9b263e2f6d2d6c7b5ec6".parse().unwrap();
+
+	let mut params = ActionParams::default();
+	params.address = address.clone();
+	params.gas = U256::from(100_000);
+	params.code = Some(code.clone());
+	params.data = Some(vec![
+		0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d,
+		0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b,
+	]);
+
+	let gas_left = {
+		let mut interpreter = wasm_interpreter();
+		test_finalize(interpreter.exec(params, &mut ext)).unwrap()
+	};
+
+	// 0 -> not 0
+	assert_eq!(gas_left, U256::from(74_410));
+
+	// #2
+
+	let mut params = ActionParams::default();
+	params.address = address.clone();
+	params.gas = U256::from(100_000);
+	params.code = Some(code.clone());
+	params.data = Some(vec![
+		0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d, 0x9d,
+		0x6b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b, 0x7b,
+	]);
+
+	let gas_left = {
+		let mut interpreter = wasm_interpreter();
+		test_finalize(interpreter.exec(params, &mut ext)).unwrap()
+	};
+
+	// not 0 -> not 0
+	assert_eq!(gas_left, U256::from(89_410));
+}
+
 // This test checks the ability of wasm contract to invoke
 // varios blockchain runtime methods
 #[test]