Gas Optimizations

[code423n4]

C4-001 : Adding unchecked directive can save gas

Impact - Gas Optimization

Using the unchecked keyword to avoid redundant arithmetic underflow/overflow checks to save gas when an underflow/overflow cannot happen. E.g. 'unchecked' can be applied in the following lines of code since there are require statements before to ensure the arithmetic operations would not cause an integer underflow or overflow. 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.

Proof of Concept

1. Navigate to the following contract function and lines.

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/AMM.sol#L676

Tools Used

Code Review

Recommended Mitigation Steps

Consider applying unchecked arithmetic where overflow/underflow is not possible.

C4-002 : > 0 can be replaced with != 0 for gas optimization

Impact - Gas Optimization

!= 0 is a cheaper operation compared to > 0, when dealing with uint.

Proof of Concept

1. Navigate to the following contract function and lines.

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/AMM.sol#L141

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/AMM.sol#L123

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/AMM.sol#L199

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/AMM.sol#L271

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/InsuranceFund.sol#L78

Tools Used

Code Review

Recommended Mitigation Steps

Use "!=0" instead of ">0" for the gas optimization.

C4-003 : ++i is more gas efficient than i++ in loops forwarding

Impact - Gas Optimization

++i is more gas efficient than i++ in loops forwarding.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L331

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L373

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L521

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L552

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L52

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L65

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L78

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L95

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L120

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L137

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L367

Tools Used

Code Review

Recommended Mitigation Steps

It is recommend to use unchecked{++i} and change i declaration to uint256.

C4-004 : Cache array length in for loops can save gas

Impact - Gas Optimization

Reading array length at each iteration of the loop takes 6 gas (3 for mload and 3 to place memory_offset) in the stack.

Caching the array length in the stack saves around 3 gas per iteration.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L331

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L373

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L521

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L552

Tools Used

Code Review

Recommended Mitigation Steps

Consider to cache array length.

C4-005 : Less than 256 uints are not gas efficient

Impact - Gas Optimization

Lower than uint256 size storage instance variables are actually less gas efficient. E.g. using uint16 does not give any efficiency, actually, it is the opposite as EVM operates on default of 256-bit values so uint16 is more expensive in this case as it needs a conversion. It only gives improvements in cases where you can pack variables together, e.g. structs.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L302

Tools Used

None

Recommended Mitigation Steps

Consider to review all uint types. Change them with uint256 If the integer is not necessary to present with uint16.`

C4-006 : State variables could be declared constant

Impact - Gas Optimization

State variables that never change can be declared constant. This can greatly reduce gas costs.

Proof of Concept

1. Navigate to the following contract variables.

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/InsuranceFund.sol#L20

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/InsuranceFund.sol#L23

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/InsuranceFund.sol#L19

Tools Used

Code Review

Recommended Mitigation Steps

Add the constant keyword for state variables whose value never change.

C4-007 : Immutable Variables

Impact - Gas Optimization

'immutable' greatly reduces gas costs. There are variables that do not change so they can be marked as immutable to greatly improve the gas costs.

Proof of Concept

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/ClearingHouse.sol#L23

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/ClearingHouse.sol#L24

Tools Used

Code Review

Recommended Mitigation Steps

Mark variables as immutable.

C4-008 : There is no need to assign default values to variables

Impact - Gas Optimization

When a variable is declared solidity assigns the default value. In case the contract assigns the value again, it costs extra gas.

Example: uint x = 0 costs more gas than uint x without having any different functionality.

Proof of Concept

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L331

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L373

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L521

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L552

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L52

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L65

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L78

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L95

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L120

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L137

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/HubbleViewer.sol#L367

Tools Used

Code Review

Recommended Mitigation Steps

uint x = 0 costs more gas than uint x without having any different functionality.

C4-009 : Cache external call results can save gas

Impact

Every call to an external contract costs a decent amount of gas. For optimization of gas usage, external call results should be cached if they are being used for more than one time.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccountHelper.sol#L25

Tools Used

Code Review

Recommended Mitigation Steps

Cache external call for the gas optimization.

C4-010 : Redundant Import

Impact - Gas Optimization

Safemath is an unnecessary import in all contracts since it is used solely for development. It can therefore be removed.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/VUSD.sol#L9

Tools Used

Code Review

Recommended Mitigation Steps

Consider to delete redundant import.

C4-011 : Gas Optimization on the Public Functions

Impact

This does not directly impact the smart contract in anyway besides cost. This is a gas optimization to reduce cost of smart contract. Calling each function, we can see that the public function uses 496 gas, while the external function uses only 261.

Proof of Concept

According to Slither Analyzer documentation (https://github.com/crytic/slither/wiki/Detector-Documentation#public-function-that-could-be-declared-external), there are functions in the contract that are never called. These functions should be declared as external in order to save gas.

Slither Detector:

external-function:

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/VUSD.sol#L69

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/InsuranceFund.sol#L104

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/InsuranceFund.sol#L108

Tools Used

Slither

Recommended Mitigation Steps

1. Get Smart Contracts from the Repository.
2. Create a python virtual environment with a stable python version.
3. Install Slither Analyzer on the python VEM.
4. Run Slither against all contracts.
5. Define public functions as an external for the gas optimization.

C4-012 : Avoid unnecessary SafeCast.toInt256() can save gas

Impact

Gas Improvement

Proof of Concept

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/ClearingHouse.sol#L332

Tools Used

None

Recommended Mitigation Steps

Avoid unnecessary SafeCast.toInt256() can save gas

C4-013 : Use of _msgSender()

Impact

The use of _msgSender() when there is no implementation of a meta transaction mechanism that uses it, such as EIP-2771, very slightly increases gas consumption.

Proof of Concept

_msgSender() is utilized three times where msg.sender could have been used in the following function.

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L115

https://github.com/code-423n4/2022-02-hubble/blob/8c157f519bc32e552f8cc832ecc75dc381faa91e/contracts/MarginAccount.sol#L140

Tools Used

None

Recommended Mitigation Steps

Replace _msgSender() with msg.sender if there is no mechanism to support meta-transactions like EIP-2771 implemented.

[atvanguard]

Good report.