Y2k Finance contest - gianganhnguyen's results

1. [G-1] ++i cost less gas compare i++ in for loops

File Vault.sol, line 443:

for (uint256 i = 0; i < epochsLength(); i++) {
   ...
}

Becomes:

for (uint256 i = 0; i < epochsLength(); ++i) {
    ...
}

2. [G-2] Cache the length of arrays in the loops

File Vault.sol, line 443:

for (uint256 i = 0; i < epochsLength(); i++) {
   ...
}

Becomes:

uint256 epochsLength = epochsLength();
for (uint256 i = 0; i < epochsLength; ++i) {
   ...
}

3. [G-3] Using uncheck blocks to save gas - increments in for loop can be uncheck

File Vault.sol, line 443:

for (uint256 i = 0; i < epochsLength(); i++) {
   ...
}

Becomes:

uint256 epochsLength = epochsLength();
for (uint256 i = 0; i < epochsLength ;) {
      ...
      unchecked { ++i; }
  }

4. [G-4] Initialize uint256 <variable>; is cheaper than uint256 <variable> = 0

File Vault.sol, line 443:

for (uint256 i = 0; i < epochsLength(); i++) {
   ...
}

Becomes:

for (uint256 i; i < epochsLength(); i++) {
      ...
  }

File StakingRewards.sol, line 36:

uint256 public periodFinish = 0;

Becomes:

uint256 public periodFinish;

5. [G-5] Using uncheck blocks to save gas

Solidity version 0.8+ comes with implicit overflow and underflow checks on unsigned integers. When an overflow or an underflow isn’t possible (as an example, when a comparison is made before the arithmetic operation), some gas can be saved by using an unchecked block

File PegOracle.sol, line 67-74:

if (price1 > price2) {
   nowPrice = (price2 * 10000) / price1;
} else {
   nowPrice = (price1 * 10000) / price2;
}

int256 decimals10 = int256(10**(18 - priceFeed1.decimals()));
nowPrice = nowPrice * decimals10;

Becomes:

unchecked {
  if (price1 > price2) {
     nowPrice = (price2 * 10000) / price1;
  } else {
     nowPrice = (price1 * 10000) / price2;
  }

  int256 decimals10 = int256(10**(18 - priceFeed1.decimals()));
  nowPrice = nowPrice * decimals10;
}

File Controller.sol, line 277:

bool isSequencerUp = answer == 0;

Becomes:

bool isSequencerUp;
unchecked {
  isSequencerUp = answer == 0;
}

File Controller.sol, line 283:

uint256 timeSinceUp = block.timestamp - startedAt;

Becomes:

uint256 timeSinceUp;
unchecked {
  timeSinceUp = block.timestamp - startedAt;
}

File Controller.sol, line 299, 300:

uint256 decimals = 10**(18-(priceFeed.decimals()));
price = price * int256(decimals);

Becomes:

uint256 decimals;
unchecked {
  decimals = 10**(18-(priceFeed.decimals()));
  price = price * int256(decimals);
}

File Vault.sol, line 266:

return (amount * epochFee[_epoch]) / 1000;

Becomes:

unchecked {
  return (amount * epochFee[_epoch]) / 1000;
}

Instances include:

File Vault.sol, line 399, 407, 419

6. [G-6] Using temporary memory

File Controller.sol, line 96-99:

if(
   vault.strikePrice() < getLatestPrice(vault.tokenInsured())
   )
   revert PriceNotAtStrikePrice(getLatestPrice(vault.tokenInsured()));

Becomes:

int256 nowPrice = getLatestPrice(vault.tokenInsured());
if(
   vault.strikePrice() < nowPrice
   )
   revert PriceNotAtStrikePrice(nowPrice);

File Controller.sol, line 199-206:

if(
   vaultFactory.getVaults(marketIndex).length != VAULTS_LENGTH)
       revert MarketDoesNotExist(marketIndex);
if(
   block.timestamp < epochEnd)
   revert EpochNotExpired();

address[] memory vaultsAddress = vaultFactory.getVaults(marketIndex);

Becomes:

address[] memory vaultsAddress = vaultFactory.getVaults(marketIndex);

if(
   vaultsAddress.length != VAULTS_LENGTH)
       revert MarketDoesNotExist(marketIndex);
if(
   block.timestamp < epochEnd)
   revert EpochNotExpired();