Fix storage fee

src/neo/SmartContract/ApplicationEngine.Storage.cs

@@ -100,10 +100,12 @@ private void PutExInternal(StorageContext context, byte[] key, byte[] value, Sto
             else
             {
                 if (item.IsConstant) throw new InvalidOperationException();
-                if (value.Length <= item.Value.Length)
+                if (value.Length == 0)
                     newDataSize = 1;
+                else if (value.Length <= item.Value.Length)
+                    newDataSize = (value.Length - 1) / 4 + 1;
                 else
-                    newDataSize = value.Length - item.Value.Length;
+                    newDataSize = (item.Value.Length - 1) / 4 + 1 + value.Length - item.Value.Length;
             }
             AddGas(newDataSize * StoragePrice);
 

tests/neo.UnitTests/SmartContract/UT_InteropPrices.cs

@@ -145,7 +145,7 @@ public void ApplicationEngineReusedStorage_PartialReuse()
                 var setupPrice = ae.GasConsumed;
                 debugger.StepInto();
                 debugger.StepInto();
-                (ae.GasConsumed - setupPrice).Should().Be(1 * ApplicationEngine.StoragePrice);
+                (ae.GasConsumed - setupPrice).Should().Be((oldValue.Length / 4 + value.Length - oldValue.Length) * ApplicationEngine.StoragePrice);
             }
         }
 
@@ -185,7 +185,7 @@ public void ApplicationEngineReusedStorage_PartialReuseTwice()
                 debugger.StepInto(); //syscall Storage.GetContext
                 var setupPrice = ae.GasConsumed;
                 debugger.StepInto(); //syscall Storage.Put
-                (ae.GasConsumed - setupPrice).Should().Be(1 * ApplicationEngine.StoragePrice); // = PUT basic fee
+                (ae.GasConsumed - setupPrice).Should().Be((sItem.Value.Length / 4 + 1) * ApplicationEngine.StoragePrice); // = PUT basic fee
             }
         }