Use unchecked math and cache values

[code423n4]

Handle

pauliax

Vulnerability details

Impact

'unchecked' directive can be used where an underflow/overflow cannot happen, e.g. here:

  if (amountEth < msg.value) {
    WETH.withdraw(msg.value-amountEth);
    payable(to).call{value: msg.value-amountEth};
  }

Also, to reduce gas usage, msg.value-amountEth should be cached and not re-calculated several times.