Adding unchecked directive can save gas

[code423n4]

Handle

WatchPug

Vulnerability details

Adding unchecked directive can save gas

For the arithmetic operations that will never over/underflow, using the unchecked directive (Solidity v0.8 has default overflow/underflow checks) can save some gas from the unnecessary internal over/underflow checks.

For example:

1. PrizePool.sol#award()

https://github.com/pooltogether/v4-core/blob/055335bf9b09e3f4bbe11a788710dd04d827bf37/contracts/prize-pool/PrizePool.sol#L210-L225

function award(address _to, uint256 _amount) external override onlyPrizeStrategy {
    if (_amount == 0) {
        return;
    }

    uint256 currentAwardBalance = _currentAwardBalance;

    require(_amount <= currentAwardBalance, "PrizePool/award-exceeds-avail");
    _currentAwardBalance = currentAwardBalance - _amount;

    ITicket _ticket = ticket;

    _mint(_to, _amount, _ticket);

    emit Awarded(_to, _ticket, _amount);
}

currentAwardBalance - _amount; will never underflow.

2. PrizeDistributor.sol#claim()

https://github.com/pooltogether/v4-core/blob/055335bf9b09e3f4bbe11a788710dd04d827bf37/contracts/PrizeDistributor.sol#L74-L77

if (payout > oldPayout) {
    payoutDiff = payout - oldPayout;
    _setDrawPayoutBalanceOf(_user, drawId, payout);
}

payout - oldPayout will never underflow.

[asselstine]

https://github.com/pooltogether/v4-core/pull/225

[GalloDaSballo]

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