Use signed 256-bit integer for sstore gas refund substate

ethcore/evm/src/interpreter/gasometer.rs

@@ -403,7 +403,7 @@ fn calculate_eip1283_sstore_gas<Gas: evm::CostType>(schedule: &Schedule, origina
 }
 
 pub fn handle_eip1283_sstore_clears_refund(ext: &mut vm::Ext, original: &U256, current: &U256, new: &U256) {
-	let sstore_clears_schedule = U256::from(ext.schedule().sstore_refund_gas);
+	let sstore_clears_schedule = ext.schedule().sstore_refund_gas;
 
 	if current == new {
 		// 1. If current value equals new value (this is a no-op), 200 gas is deducted.
@@ -438,11 +438,11 @@ pub fn handle_eip1283_sstore_clears_refund(ext: &mut vm::Ext, original: &U256, c
 				// 2.2.2. If original value equals new value (this storage slot is reset)
 				if original.is_zero() {
 					// 2.2.2.1. If original value is 0, add 19800 gas to refund counter.
-					let refund = U256::from(ext.schedule().sstore_set_gas - ext.schedule().sload_gas);
+					let refund = ext.schedule().sstore_set_gas - ext.schedule().sload_gas;
 					ext.add_sstore_refund(refund);
 				} else {
 					// 2.2.2.2. Otherwise, add 4800 gas to refund counter.
-					let refund = U256::from(ext.schedule().sstore_reset_gas - ext.schedule().sload_gas);
+					let refund = ext.schedule().sstore_reset_gas - ext.schedule().sload_gas;
 					ext.add_sstore_refund(refund);
 				}
 			}

ethcore/evm/src/interpreter/mod.rs

@@ -720,7 +720,7 @@ impl<Cost: CostType> Interpreter<Cost> {
 					gasometer::handle_eip1283_sstore_clears_refund(ext, &original_val, &current_val, &val);
 				} else {
 					if !current_val.is_zero() && val.is_zero() {
-						let sstore_clears_schedule = U256::from(ext.schedule().sstore_refund_gas);
+						let sstore_clears_schedule = ext.schedule().sstore_refund_gas;
 						ext.add_sstore_refund(sstore_clears_schedule);
 					}
 				}

ethcore/evm/src/tests.rs

@@ -716,7 +716,7 @@ fn test_jumps(factory: super::Factory) {
 		test_finalize(vm.exec(&mut ext).ok().unwrap()).unwrap()
 	};
 
-	assert_eq!(ext.sstore_clears, U256::from(ext.schedule().sstore_refund_gas));
+	assert_eq!(ext.sstore_clears, ext.schedule().sstore_refund_gas as i128);
 	assert_store(&ext, 0, "0000000000000000000000000000000000000000000000000000000000000000"); // 5!
 	assert_store(&ext, 1, "0000000000000000000000000000000000000000000000000000000000000078"); // 5!
 	assert_eq!(gas_left, U256::from(54_117));

ethcore/src/executive.rs

@@ -1091,7 +1091,8 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 		let schedule = self.schedule;
 
 		// refunds from SSTORE nonzero -> zero
-		let sstore_refunds = substate.sstore_clears_refund;
+		assert!(substate.sstore_clears_refund >= 0, "On transaction level, sstore clears refund cannot go below zero.");
+		let sstore_refunds = U256::from(substate.sstore_clears_refund as u64);
 		// refunds from contract suicides
 		let suicide_refunds = U256::from(schedule.suicide_refund_gas) * U256::from(substate.suicides.len());
 		let refunds_bound = sstore_refunds + suicide_refunds;
@@ -2095,7 +2096,7 @@ mod tests {
 		let gas_used = gas - gas_left;
 		// sstore: 0 -> (1) -> () -> (1 -> 0 -> 1)
 		assert_eq!(gas_used, U256::from(41860));
-		assert_eq!(refund, U256::from(19800));
+		assert_eq!(refund, 19800);
 
 		assert_eq!(state.storage_at(&operating_address, &k).unwrap(), H256::from(U256::from(1)));
 		// Test a call via top-level -> y2 -> x2
@@ -2113,7 +2114,7 @@ mod tests {
 		let gas_used = gas - gas_left;
 		// sstore: 1 -> (1) -> () -> (0 -> 1 -> 0)
 		assert_eq!(gas_used, U256::from(11860));
-		assert_eq!(refund, U256::from(19800));
+		assert_eq!(refund, 19800);
 	}
 
 	fn wasm_sample_code() -> Arc<Vec<u8>> {

ethcore/src/externalities.rs

@@ -394,12 +394,12 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for Externalities<'a, T, V, B>
 		self.depth
 	}
 
-	fn add_sstore_refund(&mut self, value: U256) {
-		self.substate.sstore_clears_refund = self.substate.sstore_clears_refund.saturating_add(value);
+	fn add_sstore_refund(&mut self, value: usize) {
+		self.substate.sstore_clears_refund += value as i128;
 	}
 
-	fn sub_sstore_refund(&mut self, value: U256) {
-		self.substate.sstore_clears_refund = self.substate.sstore_clears_refund.saturating_sub(value);
+	fn sub_sstore_refund(&mut self, value: usize) {
+		self.substate.sstore_clears_refund -= value as i128;
 	}
 
 	fn trace_next_instruction(&mut self, pc: usize, instruction: u8, current_gas: U256) -> bool {

ethcore/src/json_tests/executive.rs

@@ -218,11 +218,11 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for TestExt<'a, T, V, B>
 		false
 	}
 
-	fn add_sstore_refund(&mut self, value: U256) {
+	fn add_sstore_refund(&mut self, value: usize) {
 		self.ext.add_sstore_refund(value)
 	}
 
-	fn sub_sstore_refund(&mut self, value: U256) {
+	fn sub_sstore_refund(&mut self, value: usize) {
 		self.ext.sub_sstore_refund(value)
 	}
 }

ethcore/src/state/substate.rs

@@ -16,7 +16,7 @@
 
 //! Execution environment substate.
 use std::collections::HashSet;
-use ethereum_types::{U256, Address};
+use ethereum_types::Address;
 use log_entry::LogEntry;
 use evm::{Schedule, CleanDustMode};
 use super::CleanupMode;
@@ -35,7 +35,7 @@ pub struct Substate {
 	pub logs: Vec<LogEntry>,
 
 	/// Refund counter of SSTORE.
-	pub sstore_clears_refund: U256,
+	pub sstore_clears_refund: i128,
 
 	/// Created contracts.
 	pub contracts_created: Vec<Address>,
@@ -52,7 +52,7 @@ impl Substate {
 		self.suicides.extend(s.suicides);
 		self.touched.extend(s.touched);
 		self.logs.extend(s.logs);
-		self.sstore_clears_refund = self.sstore_clears_refund + s.sstore_clears_refund;
+		self.sstore_clears_refund += s.sstore_clears_refund;
 		self.contracts_created.extend(s.contracts_created);
 	}
 

ethcore/vm/src/ext.rs

@@ -151,10 +151,10 @@ pub trait Ext {
 	fn depth(&self) -> usize;
 
 	/// Increments sstore refunds counter.
-	fn add_sstore_refund(&mut self, value: U256);
+	fn add_sstore_refund(&mut self, value: usize);
 
 	/// Decrements sstore refunds counter.
-	fn sub_sstore_refund(&mut self, value: U256);
+	fn sub_sstore_refund(&mut self, value: usize);
 
 	/// Decide if any more operations should be traced. Passthrough for the VM trace.
 	fn trace_next_instruction(&mut self, _pc: usize, _instruction: u8, _current_gas: U256) -> bool { false }

ethcore/vm/src/tests.rs

@@ -57,7 +57,7 @@ pub struct FakeExt {
 	pub store: HashMap<H256, H256>,
 	pub suicides: HashSet<Address>,
 	pub calls: HashSet<FakeCall>,
-	pub sstore_clears: U256,
+	pub sstore_clears: i128,
 	pub depth: usize,
 	pub blockhashes: HashMap<U256, H256>,
 	pub codes: HashMap<Address, Arc<Bytes>>,
@@ -231,12 +231,12 @@ impl Ext for FakeExt {
 		self.is_static
 	}
 
-	fn add_sstore_refund(&mut self, value: U256) {
-		self.sstore_clears = self.sstore_clears + value;
+	fn add_sstore_refund(&mut self, value: usize) {
+		self.sstore_clears += value as i128;
 	}
 
-	fn sub_sstore_refund(&mut self, value: U256) {
-		self.sstore_clears = self.sstore_clears - value;
+	fn sub_sstore_refund(&mut self, value: usize) {
+		self.sstore_clears -= value as i128;
 	}
 
 	fn trace_next_instruction(&mut self, _pc: usize, _instruction: u8, _gas: U256) -> bool {

ethcore/wasm/src/runtime.rs

@@ -285,7 +285,7 @@ impl<'a> Runtime<'a> {
 		self.ext.set_storage(key, val).map_err(|_| Error::StorageUpdateError)?;
 
 		if former_val != H256::zero() && val == H256::zero() {
-			let sstore_clears_schedule = U256::from(self.schedule().sstore_refund_gas);
+			let sstore_clears_schedule = self.schedule().sstore_refund_gas;
 			self.ext.add_sstore_refund(sstore_clears_schedule);
 		}