Use signed 256-bit integer for sstore gas refund substate (#9746)

* Add signed refund

* Use signed 256-bit integer for sstore gas refund substate

* Fix tests

* Remove signed mod and use i128 directly

* Fix evm test case casting

* Fix jsontests ext signature

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);
 	}