[NC-1579] EIP-1283: Net gas metering for SSTORE (#10)

As per EIP-1283:  https://eips.ethereum.org/EIPS/eip-1283
Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

ethereum/core/src/main/java/net/consensys/pantheon/ethereum/core/AbstractWorldUpdater.java

@@ -65,6 +65,11 @@ public abstract class AbstractWorldUpdater<W extends WorldView, A extends Accoun
     return world.get(address);
   }
 
+  @Override
+  public Account getOriginalAccount(final Address address) {
+    return world.get(address);
+  }
+
   @Override
   public MutableAccount getMutable(final Address address) {
     // We may have updated it already, so check that first.

ethereum/core/src/main/java/net/consensys/pantheon/ethereum/core/WorldUpdater.java

@@ -61,10 +61,18 @@ public interface WorldUpdater extends MutableWorldView {
    *
    * @param address the address of the account.
    * @return the account {@code address} as modifiable object, or {@code null} if the account does
-   *     not exists.
+   *     not exist.
    */
   MutableAccount getMutable(Address address);
 
+  /**
+   * Retrieve the original account, prior to any modifications made by this updater.
+   *
+   * @param address the address of the account.
+   * @return the account {@code address} or {@code null} if the account does not exist.
+   */
+  Account getOriginalAccount(Address address);
+
   /**
    * Deletes the provided account.
    *

ethereum/core/src/main/java/net/consensys/pantheon/ethereum/mainnet/ConstantinopleGasCalculator.java

@@ -5,8 +5,19 @@ import net.consensys.pantheon.ethereum.vm.MessageFrame;
 import net.consensys.pantheon.util.bytes.Bytes32;
 import net.consensys.pantheon.util.uint.UInt256;
 
+import java.util.function.Supplier;
+
 public class ConstantinopleGasCalculator extends SpuriousDragonGasCalculator {
 
+  private static final Gas SSTORE_NO_OP_COST = Gas.of(200);
+  private static final Gas SSTORE_ADDITIONAL_WRITE_COST = Gas.of(200);
+  private static final Gas SSTORE_FIRST_DIRTY_NEW_STORAGE_COST = Gas.of(20_000);
+  private static final Gas SSTORE_FIRST_DIRTY_EXISTING_STORAGE_COST = Gas.of(5_000);
+  private static final Gas STORAGE_RESET_REFUND_AMOUNT = Gas.of(15_000);
+  private static final Gas NEGATIVE_STORAGE_RESET_REFUND_AMOUNT = Gas.of(-15_000);
+  private static final Gas SSTORE_DIRTY_RETURN_TO_UNUSED_REFUND_AMOUNT = Gas.of(19800);
+  private static final Gas SSTORE_DIRTY_RETURN_TO_ORIGINAL_VALUE_REFUND_AMOUNT = Gas.of(4800);
+
   @Override
   public Gas create2OperationGasCost(final MessageFrame frame) {
     final UInt256 initCodeLength = frame.getStackItem(2).asUInt256();
@@ -14,4 +25,66 @@ public class ConstantinopleGasCalculator extends SpuriousDragonGasCalculator {
     final Gas initCodeHashCost = SHA3_OPERATION_WORD_GAS_COST.times(Gas.of(numWords));
     return createOperationGasCost(frame).plus(initCodeHashCost);
   }
+
+  @Override
+  // As per https://eips.ethereum.org/EIPS/eip-1283
+  public Gas calculateStorageCost(
+      final Supplier<UInt256> originalValueSupplier,
+      final UInt256 currentValue,
+      final UInt256 newValue) {
+
+    if (currentValue.equals(newValue)) {
+      return SSTORE_NO_OP_COST;
+    } else {
+      final UInt256 originalValue = originalValueSupplier.get();
+      if (originalValue.equals(currentValue)) {
+        return originalValue.isZero()
+            ? SSTORE_FIRST_DIRTY_NEW_STORAGE_COST
+            : SSTORE_FIRST_DIRTY_EXISTING_STORAGE_COST;
+      } else {
+        return SSTORE_ADDITIONAL_WRITE_COST;
+      }
+    }
+  }
+
+  @Override
+  // As per https://eips.ethereum.org/EIPS/eip-1283
+  public Gas calculateStorageRefundAmount(
+      final Supplier<UInt256> originalValueSupplier,
+      final UInt256 currentValue,
+      final UInt256 newValue) {
+
+    if (currentValue.equals(newValue)) {
+      return Gas.ZERO;
+    } else {
+      final UInt256 originalValue = originalValueSupplier.get();
+      if (originalValue.equals(currentValue)) {
+        if (originalValue.isZero()) {
+          return Gas.ZERO;
+        } else if (newValue.isZero()) {
+          return STORAGE_RESET_REFUND_AMOUNT;
+        } else {
+          return Gas.ZERO;
+        }
+      } else {
+        Gas refund = Gas.ZERO;
+        if (!originalValue.isZero()) {
+          if (currentValue.isZero()) {
+            refund = NEGATIVE_STORAGE_RESET_REFUND_AMOUNT;
+          } else if (newValue.isZero()) {
+            refund = STORAGE_RESET_REFUND_AMOUNT;
+          }
+        }
+
+        if (originalValue.equals(newValue)) {
+          refund =
+              refund.plus(
+                  originalValue.isZero()
+                      ? SSTORE_DIRTY_RETURN_TO_UNUSED_REFUND_AMOUNT
+                      : SSTORE_DIRTY_RETURN_TO_ORIGINAL_VALUE_REFUND_AMOUNT);
+        }
+        return refund;
+      }
+    }
+  }
 }

ethereum/core/src/main/java/net/consensys/pantheon/ethereum/mainnet/FrontierGasCalculator.java

@@ -12,6 +12,8 @@ import net.consensys.pantheon.util.bytes.Bytes32;
 import net.consensys.pantheon.util.bytes.BytesValue;
 import net.consensys.pantheon.util.uint.UInt256;
 
+import java.util.function.Supplier;
+
 public class FrontierGasCalculator implements GasCalculator {
 
   private static final Gas TX_DATA_ZERO_COST = Gas.of(4L);
@@ -398,18 +400,17 @@ public class FrontierGasCalculator implements GasCalculator {
   }
 
   @Override
-  public Gas getStorageResetGasCost() {
-    return STORAGE_RESET_GAS_COST;
-  }
-
-  @Override
-  public Gas getStorageSetGasCost() {
-    return STORAGE_SET_GAS_COST;
+  public Gas calculateStorageCost(
+      final Supplier<UInt256> originalValue, final UInt256 currentValue, final UInt256 newValue) {
+    return !newValue.isZero() && currentValue.isZero()
+        ? STORAGE_SET_GAS_COST
+        : STORAGE_RESET_GAS_COST;
   }
 
   @Override
-  public Gas getStorageResetRefundAmount() {
-    return STORAGE_RESET_REFUND_AMOUNT;
+  public Gas calculateStorageRefundAmount(
+      final Supplier<UInt256> originalValue, final UInt256 currentValue, final UInt256 newValue) {
+    return newValue.isZero() && !currentValue.isZero() ? STORAGE_RESET_REFUND_AMOUNT : Gas.ZERO;
   }
 
   @Override

ethereum/core/src/main/java/net/consensys/pantheon/ethereum/vm/GasCalculator.java

@@ -20,12 +20,13 @@ import net.consensys.pantheon.ethereum.vm.operations.MLoadOperation;
 import net.consensys.pantheon.ethereum.vm.operations.MStore8Operation;
 import net.consensys.pantheon.ethereum.vm.operations.MStoreOperation;
 import net.consensys.pantheon.ethereum.vm.operations.SLoadOperation;
-import net.consensys.pantheon.ethereum.vm.operations.SStoreOperation;
 import net.consensys.pantheon.ethereum.vm.operations.SelfDestructOperation;
 import net.consensys.pantheon.ethereum.vm.operations.Sha3Operation;
 import net.consensys.pantheon.util.bytes.BytesValue;
 import net.consensys.pantheon.util.uint.UInt256;
 
+import java.util.function.Supplier;
+
 /**
  * Provides various gas cost lookups and calculations used during block processing.
  *
@@ -331,25 +332,25 @@ public interface GasCalculator {
   Gas getSloadOperationGasCost();
 
   /**
-   * Returns the cost for clearing a value in a {@link SStoreOperation}.
-   *
-   * @return the cost for clearing a value in a storage store operation
-   */
-  Gas getStorageResetGasCost();
-
-  /**
-   * Returns the cost for setting a value in a {@link SStoreOperation}.
+   * Returns the cost for an SSTORE operation.
    *
-   * @return the cost for setting a value in a storage store operation
+   * @param originalValue supplies the value from prior to this transaction
+   * @param currentValue the current value in the affected storage location
+   * @param newValue the new value to be stored
+   * @return the gas cost for the SSTORE operation
    */
-  Gas getStorageSetGasCost();
+  Gas calculateStorageCost(Supplier<UInt256> originalValue, UInt256 currentValue, UInt256 newValue);
 
   /**
-   * Returns the refund amount for clearing a storage location in a {@link SStoreOperation}.
+   * Returns the refund amount for an SSTORE operation.
    *
-   * @return the refund amount for clearing a storage store operation
+   * @param originalValue supplies the value from prior to this transaction
+   * @param currentValue the current value in the affected storage location
+   * @param newValue the new value to be stored
+   * @return the gas refund for the SSTORE operation
    */
-  Gas getStorageResetRefundAmount();
+  Gas calculateStorageRefundAmount(
+      Supplier<UInt256> originalValue, UInt256 currentValue, UInt256 newValue);
 
   /**
    * Returns the refund amount for deleting an account in a {@link SelfDestructOperation}.

ethereum/core/src/main/java/net/consensys/pantheon/ethereum/vm/operations/SStoreOperation.java

@@ -22,18 +22,15 @@ public class SStoreOperation extends AbstractOperation {
   @Override
   public Gas cost(final MessageFrame frame) {
     final UInt256 key = frame.getStackItem(0).asUInt256();
-    final UInt256 value = frame.getStackItem(1).asUInt256();
+    final UInt256 newValue = frame.getStackItem(1).asUInt256();
 
     final Account account = frame.getWorldState().get(frame.getRecipientAddress());
     // Setting storage value to non-zero from zero (i.e. nothing currently at this location) vs.
     // resetting an existing value.
-    final UInt256 storedValue = account.getStorageValue(key);
+    final UInt256 currentValue = account.getStorageValue(key);
 
-    if (!value.isZero() && storedValue.isZero()) {
-      return gasCalculator().getStorageSetGasCost();
-    } else {
-      return gasCalculator().getStorageResetGasCost();
-    }
+    return gasCalculator()
+        .calculateStorageCost(() -> getOriginalValue(frame, key), currentValue, newValue);
   }
 
   @Override
@@ -45,9 +42,11 @@ public class SStoreOperation extends AbstractOperation {
     assert account != null : "VM account should exists";
 
     // Increment the refund counter.
-    if (value.isZero() && !account.getStorageValue(key).isZero()) {
-      frame.incrementGasRefund(gasCalculator().getStorageResetRefundAmount());
-    }
+    final UInt256 originalValue = getOriginalValue(frame, key);
+    final UInt256 currentValue = account.getStorageValue(key);
+    frame.incrementGasRefund(
+        gasCalculator()
+            .calculateStorageRefundAmount(() -> getOriginalValue(frame, key), currentValue, value));
 
     account.setStorageValue(key.copy(), value.copy());
   }
@@ -61,4 +60,10 @@ public class SStoreOperation extends AbstractOperation {
         ? Optional.of(ExceptionalHaltReason.ILLEGAL_STATE_CHANGE)
         : Optional.empty();
   }
+
+  private UInt256 getOriginalValue(final MessageFrame frame, final UInt256 key) {
+    final Account originalAccount =
+        frame.getWorldState().getOriginalAccount(frame.getRecipientAddress());
+    return originalAccount != null ? originalAccount.getStorageValue(key) : UInt256.ZERO;
+  }
 }

ethereum/core/src/main/java/net/consensys/pantheon/ethereum/worldstate/DebuggableMutableWorldState.java

@@ -156,5 +156,11 @@ public class DebuggableMutableWorldState extends DefaultMutableWorldState {
       record(address);
       return wrapped.get(address);
     }
+
+    @Override
+    public Account getOriginalAccount(final Address address) {
+      record(address);
+      return wrapped.getOriginalAccount(address);
+    }
   }
 }

ethereum/core/src/test-support/java/net/consensys/pantheon/ethereum/core/ExecutionContextTestFixture.java

@@ -22,14 +22,18 @@ public class ExecutionContextTestFixture {
   private final WorldStateArchive stateArchive =
       new WorldStateArchive(new KeyValueStorageWorldStateStorage(keyValueStorage));
 
-  ProtocolSchedule<Void> protocolSchedule =
-      MainnetProtocolSchedule.create(2, 3, 10, 11, 12, -1, 42);
+  ProtocolSchedule<Void> protocolSchedule;
   ProtocolContext<Void> protocolContext = new ProtocolContext<>(blockchain, stateArchive, null);
 
   public ExecutionContextTestFixture() {
+    this(MainnetProtocolSchedule.create(2, 3, 10, 11, 12, -1, 42));
+  }
+
+  public ExecutionContextTestFixture(final ProtocolSchedule<Void> protocolSchedule) {
     GenesisConfig.mainnet()
         .writeStateTo(
             new DefaultMutableWorldState(new KeyValueStorageWorldStateStorage(keyValueStorage)));
+    this.protocolSchedule = protocolSchedule;
   }
 
   public Block getGenesis() {

ethereum/core/src/test-support/java/net/consensys/pantheon/ethereum/core/TestCodeExecutor.java

@@ -0,0 +1,90 @@
+package net.consensys.pantheon.ethereum.core;
+
+import net.consensys.pantheon.crypto.SECP256K1.Signature;
+import net.consensys.pantheon.ethereum.db.WorldStateArchive;
+import net.consensys.pantheon.ethereum.mainnet.MainnetMessageCallProcessor;
+import net.consensys.pantheon.ethereum.mainnet.PrecompileContractRegistry;
+import net.consensys.pantheon.ethereum.mainnet.ProtocolSchedule;
+import net.consensys.pantheon.ethereum.mainnet.ProtocolSpec;
+import net.consensys.pantheon.ethereum.vm.Code;
+import net.consensys.pantheon.ethereum.vm.MessageFrame;
+import net.consensys.pantheon.ethereum.vm.MessageFrame.Type;
+import net.consensys.pantheon.ethereum.vm.OperationTracer;
+import net.consensys.pantheon.util.bytes.BytesValue;
+
+import java.math.BigInteger;
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.function.Consumer;
+
+public class TestCodeExecutor {
+
+  private final ExecutionContextTestFixture fixture;
+  private final BlockHeader blockHeader = new BlockHeaderTestFixture().number(13).buildHeader();
+  private static final Address SENDER_ADDRESS = AddressHelpers.ofValue(244259721);
+
+  public TestCodeExecutor(final ProtocolSchedule<Void> protocolSchedule) {
+    fixture = new ExecutionContextTestFixture(protocolSchedule);
+  }
+
+  public MessageFrame executeCode(
+      final String code, final long gasLimit, final Consumer<MutableAccount> accountSetup) {
+    final ProtocolSpec<Void> protocolSpec = fixture.getProtocolSchedule().getByBlockNumber(0);
+    final WorldUpdater worldState =
+        createInitialWorldState(accountSetup, fixture.getStateArchive());
+    final Deque<MessageFrame> messageFrameStack = new ArrayDeque<>();
+
+    final MainnetMessageCallProcessor messageCallProcessor =
+        new MainnetMessageCallProcessor(protocolSpec.getEvm(), new PrecompileContractRegistry());
+
+    final Transaction transaction =
+        Transaction.builder()
+            .value(Wei.ZERO)
+            .sender(SENDER_ADDRESS)
+            .signature(Signature.create(BigInteger.ONE, BigInteger.TEN, (byte) 1))
+            .gasLimit(gasLimit)
+            .to(SENDER_ADDRESS)
+            .payload(BytesValue.EMPTY)
+            .gasPrice(Wei.ZERO)
+            .nonce(0)
+            .build();
+    final MessageFrame initialFrame =
+        MessageFrame.builder()
+            .type(Type.MESSAGE_CALL)
+            .messageFrameStack(messageFrameStack)
+            .blockchain(fixture.getBlockchain())
+            .worldState(worldState)
+            .initialGas(Gas.of(gasLimit))
+            .address(SENDER_ADDRESS)
+            .originator(SENDER_ADDRESS)
+            .contract(SENDER_ADDRESS)
+            .gasPrice(transaction.getGasPrice())
+            .inputData(transaction.getPayload())
+            .sender(SENDER_ADDRESS)
+            .value(transaction.getValue())
+            .apparentValue(transaction.getValue())
+            .code(new Code(BytesValue.fromHexString(code)))
+            .blockHeader(blockHeader)
+            .depth(0)
+            .completer(c -> {})
+            .build();
+    messageFrameStack.addFirst(initialFrame);
+
+    while (!messageFrameStack.isEmpty()) {
+      messageCallProcessor.process(messageFrameStack.peekFirst(), OperationTracer.NO_TRACING);
+    }
+    return initialFrame;
+  }
+
+  private WorldUpdater createInitialWorldState(
+      final Consumer<MutableAccount> accountSetup, final WorldStateArchive stateArchive) {
+    final MutableWorldState initialWorldState = stateArchive.getMutable();
+
+    final WorldUpdater worldState = initialWorldState.updater();
+    final MutableAccount senderAccount = worldState.getOrCreate(TestCodeExecutor.SENDER_ADDRESS);
+    accountSetup.accept(senderAccount);
+    worldState.commit();
+    initialWorldState.persist();
+    return stateArchive.getMutable(initialWorldState.rootHash()).updater();
+  }
+}

ethereum/core/src/test/java/net/consensys/pantheon/ethereum/mainnet/ConstantinopleSstoreGasTest.java

@@ -0,0 +1,87 @@
+package net.consensys.pantheon.ethereum.mainnet;
+
+import static net.consensys.pantheon.util.uint.UInt256.ONE;
+import static net.consensys.pantheon.util.uint.UInt256.ZERO;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import net.consensys.pantheon.ethereum.core.Gas;
+import net.consensys.pantheon.util.uint.UInt256;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameter;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class ConstantinopleSstoreGasTest {
+
+  private static final UInt256 TWO = UInt256.of(2);
+
+  private final ConstantinopleGasCalculator gasCalculator = new ConstantinopleGasCalculator();
+
+  @Parameters(name = "original: {0}, current: {1}, new: {2}")
+  public static Object[][] scenarios() {
+    return new Object[][] {
+      // Zero no-op
+      {ZERO, ZERO, ZERO, Gas.of(200), Gas.ZERO},
+
+      // Zero fresh change
+      {ZERO, ZERO, ONE, Gas.of(20_000), Gas.ZERO},
+
+      // Dirty, reset to zero
+      {ZERO, ONE, ZERO, Gas.of(200), Gas.of(19800)},
+
+      // Dirty, changed but not reset
+      {ZERO, ONE, TWO, Gas.of(200), Gas.ZERO},
+
+      // Dirty no-op
+      {ZERO, ONE, ONE, Gas.of(200), Gas.ZERO},
+
+      // Dirty, zero no-op
+      {ONE, ZERO, ZERO, Gas.of(200), Gas.ZERO},
+
+      // Dirty, reset to non-zero
+      {ONE, ZERO, ONE, Gas.of(200), Gas.of(-15000).plus(Gas.of(4800))},
+
+      // Fresh change to zero
+      {ONE, ONE, ZERO, Gas.of(5000), Gas.of(15000)},
+
+      // Fresh change with all non-zero
+      {ONE, ONE, TWO, Gas.of(5000), Gas.ZERO},
+
+      // Dirty, clear originally set value
+      {ONE, TWO, ZERO, Gas.of(200), Gas.of(15000)},
+
+      // Non-zero no-op
+      {ONE, ONE, ONE, Gas.of(200), Gas.ZERO},
+    };
+  }
+
+  @Parameter public UInt256 originalValue;
+
+  @Parameter(value = 1)
+  public UInt256 currentValue;
+
+  @Parameter(value = 2)
+  public UInt256 newValue;
+
+  @Parameter(value = 3)
+  public Gas expectedGasCost;
+
+  @Parameter(value = 4)
+  public Gas expectedGasRefund;
+
+  @Test
+  public void shouldChargeCorrectGas() {
+    assertThat(gasCalculator.calculateStorageCost(() -> originalValue, currentValue, newValue))
+        .isEqualTo(expectedGasCost);
+  }
+
+  @Test
+  public void shouldRefundCorrectGas() {
+    assertThat(
+            gasCalculator.calculateStorageRefundAmount(() -> originalValue, currentValue, newValue))
+        .isEqualTo(expectedGasRefund);
+  }
+}

ethereum/core/src/test/java/net/consensys/pantheon/ethereum/vm/operations/ConstantinopleSStoreOperationGasCostTest.java

@@ -0,0 +1,79 @@
+package net.consensys.pantheon.ethereum.vm.operations;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import net.consensys.pantheon.ethereum.core.Gas;
+import net.consensys.pantheon.ethereum.core.TestCodeExecutor;
+import net.consensys.pantheon.ethereum.mainnet.MainnetProtocolSchedule;
+import net.consensys.pantheon.ethereum.mainnet.ProtocolSchedule;
+import net.consensys.pantheon.ethereum.vm.MessageFrame;
+import net.consensys.pantheon.ethereum.vm.MessageFrame.State;
+import net.consensys.pantheon.util.uint.UInt256;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameter;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class ConstantinopleSStoreOperationGasCostTest {
+  private static final ProtocolSchedule<Void> protocolSchedule =
+      MainnetProtocolSchedule.create(0, 0, 0, 0, 0, 0, 1);
+
+  @Parameters(name = "Code: {0}, Original: {1}")
+  public static Object[][] scenarios() {
+    // Tests specified in EIP-1283.
+    return new Object[][] {
+      {"0x60006000556000600055", 0, 412, 0},
+      {"0x60006000556001600055", 0, 20212, 0},
+      {"0x60016000556000600055", 0, 20212, 19800},
+      {"0x60016000556002600055", 0, 20212, 0},
+      {"0x60016000556001600055", 0, 20212, 0},
+      {"0x60006000556000600055", 1, 5212, 15000},
+      {"0x60006000556001600055", 1, 5212, 4800},
+      {"0x60006000556002600055", 1, 5212, 0},
+      {"0x60026000556003600055", 1, 5212, 0},
+      {"0x60026000556001600055", 1, 5212, 4800},
+      {"0x60026000556002600055", 1, 5212, 0},
+      {"0x60016000556000600055", 1, 5212, 15000},
+      {"0x60016000556002600055", 1, 5212, 0},
+      {"0x60016000556001600055", 1, 412, 0},
+      {"0x600160005560006000556001600055", 0, 40218, 19800},
+      {"0x600060005560016000556000600055", 1, 10218, 19800},
+      {"0x60026000556000600055", 1, 5212, 15000},
+    };
+  }
+
+  private TestCodeExecutor codeExecutor;
+
+  @Parameter public String code;
+
+  @Parameter(value = 1)
+  public int originalValue;
+
+  @Parameter(value = 2)
+  public int expectedGasUsed;
+
+  @Parameter(value = 3)
+  public int expectedGasRefund;
+
+  @Before
+  public void setUp() {
+    codeExecutor = new TestCodeExecutor(protocolSchedule);
+  }
+
+  @Test
+  public void shouldCalculateGasAccordingToEip1283() {
+    final long gasLimit = 1_000_000;
+    final MessageFrame frame =
+        codeExecutor.executeCode(
+            code,
+            gasLimit,
+            account -> account.setStorageValue(UInt256.ZERO, UInt256.of(originalValue)));
+    assertThat(frame.getState()).isEqualTo(State.COMPLETED_SUCCESS);
+    assertThat(frame.getRemainingGas()).isEqualTo(Gas.of(gasLimit - expectedGasUsed));
+    assertThat(frame.getGasRefund()).isEqualTo(Gas.of(expectedGasRefund));
+  }
+}