Mul speedup (#4756)

Move mul from UInt256 wrapping to direct BigInteger math.

Signed-off-by: Danno Ferrin <danno.ferrin@swirldslabs.com>

evm/src/main/java/org/hyperledger/besu/evm/EVM.java

@@ -292,8 +292,9 @@ public class EVM {
         LOG.trace("MessageFrame evaluation halted because of {}", haltReason);
         frame.setExceptionalHaltReason(Optional.of(haltReason));
         frame.setState(State.EXCEPTIONAL_HALT);
-      } else {
-        frame.decrementRemainingGas(result.getGasCost());
+      } else if (frame.decrementRemainingGas(result.getGasCost()) < 0) {
+        frame.setExceptionalHaltReason(Optional.of(ExceptionalHaltReason.INSUFFICIENT_GAS));
+        frame.setState(State.EXCEPTIONAL_HALT);
       }
       if (frame.getState() == State.CODE_EXECUTING) {
         final int currentPC = frame.getPC();

evm/src/main/java/org/hyperledger/besu/evm/frame/MessageFrame.java

@@ -350,9 +350,10 @@ public class MessageFrame {
    * Decrement the amount of remaining gas.
    *
    * @param amount The amount of gas to deduct
+   * @return the amount of gas available, after deductions.
    */
-  public void decrementRemainingGas(final long amount) {
-    this.gasRemaining -= amount;
+  public long decrementRemainingGas(final long amount) {
+    return this.gasRemaining -= amount;
   }
 
   /**

evm/src/main/java/org/hyperledger/besu/evm/operation/MulOperation.java

@@ -18,7 +18,9 @@ import org.hyperledger.besu.evm.EVM;
 import org.hyperledger.besu.evm.frame.MessageFrame;
 import org.hyperledger.besu.evm.gascalculator.GasCalculator;
 
-import org.apache.tuweni.units.bigints.UInt256;
+import java.math.BigInteger;
+
+import org.apache.tuweni.bytes.Bytes;
 
 public class MulOperation extends AbstractFixedCostOperation {
 
@@ -35,14 +37,16 @@ public class MulOperation extends AbstractFixedCostOperation {
   }
 
   public static OperationResult staticOperation(final MessageFrame frame) {
-
-    final UInt256 value0 = UInt256.fromBytes(frame.popStackItem());
-    final UInt256 value1 = UInt256.fromBytes(frame.popStackItem());
-
-    final UInt256 result = value0.multiply(value1);
+    BigInteger a = new BigInteger(1, frame.popStackItem().toArrayUnsafe());
+    BigInteger b = new BigInteger(1, frame.popStackItem().toArrayUnsafe());
+    BigInteger c = a.multiply(b);
+    byte[] cBytes = c.toByteArray();
+    Bytes result = Bytes.wrap(cBytes);
+    if (cBytes.length > 32) {
+      result = result.slice(cBytes.length - 32, 32);
+    }
 
     frame.pushStackItem(result);
-
     return mulSuccess;
   }
 }