Yieldy contest - Tomio's results

Title: Using multiple require instead && can save gas

Proof of Concept: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/LiquidityReserve.sol#L44-L47 https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Migration.sol#L20-L23 https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Staking.sol#L54-L63 https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Staking.sol#L574-L577

Recommended Mitigation Steps:

	require(_stakingToken != address(0), "Invalid address");
	require(_rewardToken != address(0), "Invalid address");

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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: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/LiquidityReserve.sol https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Staking.sol https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Yieldy.sol

Recommended Mitigation Steps: Replace require statements with custom errors.

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Title: Using != is more gas efficient

Proof of Concept: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Staking.sol#L118 https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Staking.sol#L410 https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Staking.sol#L572

Recommended Mitigation Steps: Change from > to !=

    require(_recipient.amount != 0, "Must enter valid amount");

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Title: Comparison operators

Proof of Concept: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Staking.sol#L586 https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Yieldy.sol#L190 https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Yieldy.sol#L210

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

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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: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Staking.sol#L636-L637

Recommended Mitigation Steps: Remove explicit initialization for default values.

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Title: Function rebase(): L#716 should be unchecked due to L#713

Proof of Concept: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Staking.sol#L716

Recommended Mitigation Steps: Use unchecked

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Title: Function transfer(): L#192 should be unchecked due to L#190

Proof of Concept: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Yieldy.sol#L192

Recommended Mitigation Steps: Use unchecked

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Title: Function transferFrom(): L#212 should be unchecked due to L#210

Proof of Concept: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Yieldy.sol#L212

Recommended Mitigation Steps: Use unchecked

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Title: currentCredits only used once

Proof of Concept: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Yieldy.sol#L286

Recommended Mitigation Steps: instead of caching it to currentCredits, delete L#285 and use creditBalances[_address] directly

	require(creditBalances[_address] >= creditAmount, "Not enough balance"); //@audit gas: save about 5 gas

Or

Title: Use currentCredits that already been cache instead

Proof of Concept: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/Yieldy.sol#L288

Recommended Mitigation Steps: Change to:

	currentCredits = currentCredits - creditAmount;

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Title: Expression for constant values such as a call to keccak256(), should use immutable rather than constant

Proof of Concept: https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/YieldyStorage.sol#L10-L13

Recommended Mitigation Steps: Change from constant to immutable reference: https://github.com/ethereum/solidity/issues/9232

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