implement EIP2200's SSTORE and gas cost

nimbus/db/state_db.nim

@@ -208,6 +208,10 @@ proc isDeadAccount*(db: AccountStateDB, address: EthAddress): bool =
   else:
     result = true
 
+proc getCommittedStorage*(db: AccountStateDB, address: EthAddress, slot: UInt256): UInt256 =
+  discard
+  # TODO: stub
+
 proc rootHash*(db: ReadOnlyStateDB): KeccakHash {.borrow.}
 proc getAccount*(db: ReadOnlyStateDB, address: EthAddress): Account {.borrow.}
 proc getCodeHash*(db: ReadOnlyStateDB, address: EthAddress): Hash256 {.borrow.}
@@ -220,3 +224,4 @@ proc hasCodeOrNonce*(db: ReadOnlyStateDB, address: EthAddress): bool {.borrow.}
 proc accountExists*(db: ReadOnlyStateDB, address: EthAddress): bool {.borrow.}
 proc isDeadAccount*(db: ReadOnlyStateDB, address: EthAddress): bool {.borrow.}
 proc isEmptyAccount*(db: ReadOnlyStateDB, address: EthAddress): bool {.borrow.}
+proc getCommittedStorage*(db: ReadOnlyStateDB, address: EthAddress, slot: UInt256): UInt256 {.borrow.}

nimbus/vm/interpreter/gas_costs.nim

@@ -65,6 +65,8 @@ type
     case kind*: Op
     of Sstore:
       s_isStorageEmpty*: bool
+      s_currentValue*: Uint256
+      s_originalValue*: Uint256
     of Call, CallCode, DelegateCall, StaticCall:
       c_isNewAccount*: bool
       c_gasBalance*: GasInt
@@ -247,6 +249,34 @@ template gasCosts(fork: Fork, prefix, ResultGasCostsName: untyped) =
         ClearRefundEIP2200 = FeeSchedule[RefundSclear]# clearing an originally existing storage slot
 
       # Gas sentry honoured, do the actual gas calculation based on the stored value
+      if gasParams.s_currentValue == value: # noop (1)
+        result.gasCost = NoopGasEIP2200
+        return
+
+      if gasParams.s_originalValue == gasParams.s_currentValue:
+        if gasParams.s_originalValue.isZero: # create slot (2.1.1)
+          result.gasCost = InitGasEIP2200
+          return
+
+        if value.isZero: # delete slot (2.1.2b)
+          result.gasRefund = ClearRefundEIP2200
+
+        result.gasCost = CleanGasEIP2200 # write existing slot (2.1.2)
+        return
+
+      if not gasParams.s_originalValue.isZero:
+        if gasParams.s_currentValue.isZero: # recreate slot (2.2.1.1)
+          result.gasRefund -= ClearRefundEIP2200
+        if value.isZero: # delete slot (2.2.1.2)
+          result.gasRefund += ClearRefundEIP2200
+
+      if gasParams.s_originalValue == value:
+        if gasParams.s_originalValue.isZero: # reset to original inexistent slot (2.2.2.1)
+          result.gasRefund = InitRefundEIP2200
+        else: # reset to original existing slot (2.2.2.2)
+          result.gasRefund = CleanRefundEIP2200
+
+      result.gasCost = DirtyGasEIP2200 # dirty update (2.2)
 
   func `prefix gasLog0`(currentMemSize, memOffset, memLength: GasNatural): GasInt {.nimcall.} =
     result = `prefix gasMemoryExpansion`(currentMemSize, memOffset, memLength)

nimbus/vm/interpreter/opcodes_impl.nim

@@ -933,4 +933,26 @@ op extCodeHash, inline = true:
 
 op sstoreEIP2200, inline = false, slot, value:
   checkInStaticContext(computation)
-  # TODO: stub
+  const SentryGasEIP2200   = 2300  # Minimum gas required to be present for an SSTORE call, not consumed
+
+  if computation.gasMeter.gasRemaining < SentryGasEIP2200:
+    raise newException(OutOfGas, "Gas not enough to perform EIP2200 SSTORE")
+
+  let stateDB = computation.vmState.readOnlyStateDB
+  let (currentValue, existing) = stateDB.getStorage(computation.msg.storageAddress, slot)
+
+  let
+    gasParam = GasParams(kind: Op.Sstore,
+      s_isStorageEmpty: currentValue.isZero,
+      s_currentValue: currentValue,
+      s_originalValue: stateDB.getCommittedStorage(computation.msg.storageAddress, slot)
+    )
+    (gasCost, gasRefund) = computation.gasCosts[Sstore].c_handler(value, gasParam)
+
+  computation.gasMeter.consumeGas(gasCost, &"SSTORE EIP2200: {computation.msg.storageAddress}[{slot}] -> {value} ({currentValue})")
+
+  if gasRefund > 0:
+    computation.gasMeter.refundGas(gasRefund)
+
+  computation.vmState.mutateStateDB:
+    db.setStorage(computation.msg.storageAddress, slot, value)