fixes evmc 'gasRefund'

nimbus/vm/evmc_host.nim

@@ -46,44 +46,39 @@ proc hostSetStorageImpl(ctx: Computation, address: var evmc_address,
 
   assert storageAddr == ctx.msg.contractAddress
 
-  if newValue == currValue:
-    return EVMC_STORAGE_UNCHANGED
-
-  let
-    origValue = statedb.getCommittedStorage(storageAddr, slot)
-    InitRefundEIP2200  = gasFees[ctx.fork][GasSset] - gasFees[ctx.fork][GasSload]
-    CleanRefundEIP2200 = gasFees[ctx.fork][GasSreset] - gasFees[ctx.fork][GasSload]
-    ClearRefundEIP2200 = gasFees[ctx.fork][RefundsClear]
-
   var
-    gasRefund = 0.GasInt
     status = EVMC_STORAGE_MODIFIED
+    gasRefund = 0.GasInt
+    origValue = 0.u256
+
+  block:
+    if newValue == currValue:
+      status = EVMC_STORAGE_UNCHANGED
+      break
+
+    origValue = statedb.getCommittedStorage(storageAddr, slot)
 
     if origValue == currValue or ctx.fork < FkIstanbul:
       if currValue == 0:
         status = EVMC_STORAGE_ADDED
       elif newValue == 0:
         status = EVMC_STORAGE_DELETED
-      gasRefund += ClearRefundEIP2200
     else:
       status = EVMC_STORAGE_MODIFIED_AGAIN
-    if origValue != 0:
-      if currValue == 0:
-        gasRefund -= ClearRefundEIP2200  # Can go negative
-      if newValue == 0:
-        gasRefund += ClearRefundEIP2200
-    if origValue == newValue:
-      if origValue == 0:
-        gasRefund += InitRefundEIP2200
-      else:
-        gasRefund += CleanRefundEIP2200
-
-  if gasRefund > 0:
-    ctx.gasMeter.refundGas(gasRefund)
 
     ctx.vmState.mutateStateDB:
       db.setStorage(storageAddr, slot, newValue)
 
+  let gasParam = GasParams(kind: Op.Sstore,
+      s_status: status,
+      s_currentValue: currValue,
+      s_originalValue: origValue
+    )
+  gasRefund = ctx.gasCosts[Sstore].c_handler(newValue, gasParam)[1]
+
+  if gasRefund != 0:
+    ctx.gasMeter.refundGas(gasRefund)
+
   result = status
 
 proc hostGetBalanceImpl(ctx: Computation, address: var evmc_address): evmc_uint256be {.cdecl.} =

nimbus/vm/interpreter/gas_costs.nim

@@ -222,13 +222,31 @@ template gasCosts(fork: Fork, prefix, ResultGasCostsName: untyped) =
         sstoreLoad = FeeSchedule[GasSload]
         sstoreSet  = FeeSchedule[GasSset]
         sstoreReset= FeeSchedule[GasSreset]
+        sstoreDirty= when fork >= FkIstanbul: sstoreLoad else: sstoreReset
+        InitRefundEIP2200  = FeeSchedule[GasSset] - FeeSchedule[GasSload]
+        CleanRefundEIP2200 = FeeSchedule[GasSreset] - FeeSchedule[GasSload]
+        ClearRefundEIP2200 = FeeSchedule[RefundsClear]
 
       case gasParams.s_status
       of EVMC_STORAGE_ADDED: result.gasCost = sstoreSet
-      of EVMC_STORAGE_MODIFIED, EVMC_STORAGE_DELETED: result.gasCost = sstoreReset
+      of EVMC_STORAGE_MODIFIED: result.gasCost = sstoreReset
-      of EVMC_STORAGE_UNCHANGED, EVMC_STORAGE_MODIFIED_AGAIN:
+      of EVMC_STORAGE_DELETED:
-         result.gasCost = if fork >= FkIstanbul: sstoreLoad else: sstoreReset
+        result.gasCost = sstoreReset
+        result.gasRefund += ClearRefundEIP2200
+      of EVMC_STORAGE_UNCHANGED: result.gasCost = sstoreDirty
+      of EVMC_STORAGE_MODIFIED_AGAIN:
+        result.gasCost = sstoreDirty
+        if not gasParams.s_originalValue.isZero:
+          if gasParams.s_currentValue.isZero:
+            result.gasRefund -= ClearRefundEIP2200
+          if value.isZero:
+            result.gasRefund += ClearRefundEIP2200
 
+        if gasParams.s_originalValue == value:
+          if gasParams.s_originalValue.isZero:
+            result.gasRefund += InitRefundEIP2200
+          else:
+            result.gasRefund += CleanRefundEIP2200
     else:
       when fork < FkIstanbul:
         # workaround for static evaluation not working for if expression