Only use SafeMath when necessary can save gas

[code423n4]

Handle

WatchPug

Vulnerability details

For the arithmetic operations that will never over/underflow, using SafeMath will cost more gas.

For example:

https://github.com/code-423n4/2021-11-malt/blob/c3a204a2c0f7c653c6c2dda9f4563fd1dc1cecf3/src/contracts/Auction.sol#L238-L242

    if (amountTokens > unclaimedArbTokens) {
      unclaimedArbTokens = 0;
    } else {
      unclaimedArbTokens = unclaimedArbTokens.sub(amountTokens);
    }

unclaimedArbTokens - amountTokens will never underflow.

Recommendation

Change to:

    if (amountTokens >= unclaimedArbTokens) {
      unclaimedArbTokens = 0;
    } else {
      unclaimedArbTokens -= amountTokens;
    }

https://github.com/code-423n4/2021-11-malt/blob/c3a204a2c0f7c653c6c2dda9f4563fd1dc1cecf3/src/contracts/AuctionBurnReserveSkew.sol#L76-L80

if (premiumExcess > maxBurnSpend) {
  return premiumExcess;
}

uint256 usableExcess = maxBurnSpend.sub(premiumExcess);

maxBurnSpend - premiumExcess will never underflow.

Recommendation

Change to:

if (premiumExcess > maxBurnSpend) {
  return premiumExcess;
}

uint256 usableExcess = maxBurnSpend - premiumExcess;

[GalloDaSballo]

Agree with the finding, typically safeMath adds an extra 30 / 40 gas per check, that said, it's ok to keep it to make the codebase more consistent