Y2k Finance contest - Tomio's results

Title: Set as immutable can save gas

Proof of Concept: RewardsFactory.sol#L9-L11 PegOracle.sol#L10-L11

Recommended Mitigation Steps: can be set as immutable, which already set once in the constructor

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Title: abi.encode() is less efficient than abi.encodePacked()

Proof of Concept: RewardsFactory.sol#L150

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Title: Using SafeMath for solidity >0.8

Proof of Concept: StakingRewards.sol#L29

Recommended Mitigation Steps: it's better to remove using SafeMath for uint256 for solidity >0.8 reference: https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2465

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Title: Default value initialization

Impact: If a variable is not set/initialized, it is assumed to have the default value (0, false, 0x0 etc depending on the data type). Explicitly initializing it with its default value is an anti-pattern and wastes gas.

Proof of Concept: StakingRewards.sol#L36 Vault.sol#L443

Recommended Mitigation Steps: Remove explicit initialization for default values.

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Title: Using != is more gas efficient in require statement

Proof of Concept: StakingRewards.sol#L119 PegOracle.sol#L98 PegOracle.sol#L121 Vault.sol#L187

Recommended Mitigation Steps: Change from > 0 to != 0

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Title: Comparison operators

Proof of Concept: StakingRewards.sol#L189

Recommended Mitigation Steps: Replace <= with <, and >= with > for gas optimization

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Title: Custom errors from Solidity 0.8.4 are cheaper than revert strings

Impact: Custom errors from Solidity 0.8.4 are cheaper than revert strings (cheaper deployment cost and runtime cost when the revert condition is met) while providing the same amount of information

Custom errors are defined using the error statement reference: https://blog.soliditylang.org/2021/04/21/custom-errors/

Proof of Concept: StakingRewards.sol (various line) PegOracle.sol (various line) SemiFungibleVault.sol#L118

Recommended Mitigation Steps: Replace require statements with custom errors.

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Title: Reduce the size of error messages (Long revert Strings)

Impact: Shortening revert strings to fit in 32 bytes will decrease deployment time gas and will decrease runtime gas when the revert condition is met. Revert strings that are longer than 32 bytes require at least one additional mstore, along with additional overhead for computing memory offset, etc.

Proof of Concept: StakingRewards.sol#L228 SemiFungibleVault.sol#L118

Recommended Mitigation Steps: Consider shortening the revert strings to fit in 32 bytes

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Title: Consider make constant as private to save gas

Proof of Concept: Controller.sol#L16

Recommended Mitigation Steps: I suggest changing the visibility from public to internal or private

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Title: Using == false cost more gas

Proof of Concept: Controller.sol#L93 Vault.sol#L217 Controller.sol#L211

Recommended Mitigation Steps: Change to:

    require(!vault.idExists(epochEnd));

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Title: Using *= can save gas

Proof of Concept: PegOracle.sol#L74 Controller.sol#L300

Recommended Mitigation Steps: Change to:

	nowPrice *= decimals10;

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Title: Using unchecked and prefix increment is more effective for gas saving:

Proof of Concept: Vault.sol#L443

Recommended Mitigation Steps: Change to:

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

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