Gas Optimizations #196

code423n4 · 2022-03-30T22:04:03Z

Code refactoring

The chain of getOwnBalance(), _executeSwaps(), getOwnBalance(), require(), assign, should be refactored to a common function
https://github.com/code-423n4/2022-03-lifinance/blob/699c2305fcfb6fe8862b75b26d1d8a2f46a551e6/src/Facets/NXTPFacet.sol#L91-L100
https://github.com/code-423n4/2022-03-lifinance/blob/699c2305fcfb6fe8862b75b26d1d8a2f46a551e6/src/Facets/HopFacet.sol#L102-L111
https://github.com/code-423n4/2022-03-lifinance/blob/699c2305fcfb6fe8862b75b26d1d8a2f46a551e6/src/Facets/AnyswapFacet.sol#L85-L94
https://github.com/code-423n4/2022-03-lifinance/blob/699c2305fcfb6fe8862b75b26d1d8a2f46a551e6/src/Facets/CBridgeFacet.sol#L98-L107
The same should be done for the native versions

Don't compare boolean expressions to boolean literals

if (<x> == true) => if (<x>), if (<x> == false) => if (!<x>)

File: src/Facets/DexManagerFacet.sol (line 20)

        if (s.dexWhitelist[_dex] == true) {

File: src/Facets/DexManagerFacet.sol (line 34)

            if (s.dexWhitelist[_dexs[i]] == true) {

File: src/Facets/DexManagerFacet.sol (line 47)

        if (s.dexWhitelist[_dex] == false) {

File: src/Facets/DexManagerFacet.sol (line 66)

            if (s.dexWhitelist[_dexs[i]] == false) {

File: src/Facets/Swapper.sol (line 16)

                ls.dexWhitelist[_swapData[i].approveTo] == true && ls.dexWhitelist[_swapData[i].callTo] == true,

File: src/Facets/Swapper.sol (line 16)

                ls.dexWhitelist[_swapData[i].approveTo] == true && ls.dexWhitelist[_swapData[i].callTo] == true,

Expressions for constant values such as a call to `keccak256()`, should use `immutable` rather than `constant`

See this issue for a detail description of the issue

File: src/Libraries/LibDiamond.sol (line 7)

    bytes32 internal constant DIAMOND_STORAGE_POSITION = keccak256("diamond.standard.diamond.storage");

File: src/Facets/NXTPFacet.sol (line 18)

    bytes32 internal constant NAMESPACE = keccak256("com.lifi.facets.nxtp");

File: src/Facets/HopFacet.sol (line 18)

    bytes32 internal constant NAMESPACE = keccak256("com.lifi.facets.hop");

File: src/Facets/CBridgeFacet.sol (line 18)

    bytes32 internal constant NAMESPACE = keccak256("com.lifi.facets.cbridge2");

Superfluous event fields

block.timestamp and block.number are added to event information by default so adding them manually wastes gas

File: src/Libraries/LibSwap.sol (line 26)

        uint256 timestamp

File: src/Interfaces/ILiFi.sol (line 29)

        uint256 timestamp

File: src/Interfaces/ILiFi.sol (line 37)

        uint256 timestamp

File: src/Interfaces/ILiFi.sol (line 49)

        uint256 timestamp

File: src/Interfaces/ILiFi.sol (line 60)

        uint256 timestamp

`++i`/`i++` should be `unchecked{++i}`/`unchecked{++i}` when it is not possible for them to overflow, as is the case when used in `for`- and `while`-loops

File: src/Libraries/LibDiamond.sol (line 67)

        for (uint256 facetIndex; facetIndex < _diamondCut.length; facetIndex++) {

File: src/Libraries/LibDiamond.sol (line 92)

        for (uint256 selectorIndex; selectorIndex < _functionSelectors.length; selectorIndex++) {

File: src/Libraries/LibDiamond.sol (line 110)

        for (uint256 selectorIndex; selectorIndex < _functionSelectors.length; selectorIndex++) {

File: src/Libraries/LibDiamond.sol (line 125)

        for (uint256 selectorIndex; selectorIndex < _functionSelectors.length; selectorIndex++) {

File: src/Facets/DexManagerFacet.sol (line 33)

        for (uint256 i; i < _dexs.length; i++) {

File: src/Facets/DexManagerFacet.sol (line 52)

        for (uint256 i; i < s.dexs.length; i++) {

File: src/Facets/DexManagerFacet.sol (line 65)

        for (uint256 i; i < _dexs.length; i++) {

File: src/Facets/DexManagerFacet.sol (line 70)

            for (uint256 j; j < s.dexs.length; j++) {

File: src/Facets/HopFacet.sol (line 48)

        for (uint8 i; i < _tokens.length; i++) {

File: src/Facets/Swapper.sol (line 14)

        for (uint8 i; i < _swapData.length; i++) {

File: src/Facets/DiamondLoupeFacet.sol (line 24)

        for (uint256 i; i < numFacets; i++) {

`<array>.length` should not be looked up in every loop of a `for`-loop

Even memory arrays incur the overhead of bit tests and bit shifts to calculate the array length

File: src/Libraries/LibDiamond.sol (line 67)

        for (uint256 facetIndex; facetIndex < _diamondCut.length; facetIndex++) {

File: src/Libraries/LibDiamond.sol (line 92)

        for (uint256 selectorIndex; selectorIndex < _functionSelectors.length; selectorIndex++) {

File: src/Libraries/LibDiamond.sol (line 110)

        for (uint256 selectorIndex; selectorIndex < _functionSelectors.length; selectorIndex++) {

File: src/Libraries/LibDiamond.sol (line 125)

        for (uint256 selectorIndex; selectorIndex < _functionSelectors.length; selectorIndex++) {

File: src/Facets/DexManagerFacet.sol (line 33)

        for (uint256 i; i < _dexs.length; i++) {

File: src/Facets/DexManagerFacet.sol (line 52)

        for (uint256 i; i < s.dexs.length; i++) {

File: src/Facets/DexManagerFacet.sol (line 65)

        for (uint256 i; i < _dexs.length; i++) {

File: src/Facets/DexManagerFacet.sol (line 70)

            for (uint256 j; j < s.dexs.length; j++) {

File: src/Facets/HopFacet.sol (line 48)

        for (uint8 i; i < _tokens.length; i++) {

File: src/Facets/Swapper.sol (line 14)

        for (uint8 i; i < _swapData.length; i++) {

Using `calldata` instead of `memory` for read-only arguments in `external` functions saves gas

File: src/Facets/HopFacet.sol (line 41)

        string[] memory _tokens,

File: src/Facets/HopFacet.sol (line 42)

        IHopBridge.BridgeConfig[] memory _bridgeConfigs,

`require()` or `revert()` statements that check input arguments should be at the top of the function

File: src/Libraries/LibDiamond.sol (line 86)

        require(_facetAddress != address(0), "LibDiamondCut: Add facet can't be address(0)");

File: src/Libraries/LibDiamond.sol (line 104)

        require(_facetAddress != address(0), "LibDiamondCut: Add facet can't be address(0)");

File: src/Libraries/LibDiamond.sol (line 124)

        require(_facetAddress == address(0), "LibDiamondCut: Remove facet address must be address(0)");

`internal` functions only called once can be inlined to save gas

File: src/Facets/CBridgeFacet.sol (line 176)

    function _bridge() internal view returns (address) {

`++i` costs less gas than `++i`, especially when it's used in `for`-loops (`--i`/`i--` too)

File: src/Libraries/LibDiamond.sol (line 67)

        for (uint256 facetIndex; facetIndex < _diamondCut.length; facetIndex++) {

File: src/Libraries/LibDiamond.sol (line 92)

        for (uint256 selectorIndex; selectorIndex < _functionSelectors.length; selectorIndex++) {

File: src/Libraries/LibDiamond.sol (line 110)

        for (uint256 selectorIndex; selectorIndex < _functionSelectors.length; selectorIndex++) {

File: src/Libraries/LibDiamond.sol (line 125)

        for (uint256 selectorIndex; selectorIndex < _functionSelectors.length; selectorIndex++) {

File: src/Facets/DexManagerFacet.sol (line 33)

        for (uint256 i; i < _dexs.length; i++) {

File: src/Facets/DexManagerFacet.sol (line 52)

        for (uint256 i; i < s.dexs.length; i++) {

File: src/Facets/DexManagerFacet.sol (line 65)

        for (uint256 i; i < _dexs.length; i++) {

File: src/Facets/DexManagerFacet.sol (line 70)

            for (uint256 j; j < s.dexs.length; j++) {

File: src/Facets/HopFacet.sol (line 48)

        for (uint8 i; i < _tokens.length; i++) {

File: src/Facets/Swapper.sol (line 14)

        for (uint8 i; i < _swapData.length; i++) {

File: src/Facets/DiamondLoupeFacet.sol (line 24)

        for (uint256 i; i < numFacets; i++) {

Use a more recent version of solidity

Use a solidity version of at least 0.8.10 to have external calls skip contract existence checks if the external call has a return value

File: src/Libraries/LibSwap.sol (line 2)

pragma solidity ^0.8.7;

File: src/Libraries/LibUtil.sol (line 2)

pragma solidity ^0.8.7;

File: src/Libraries/LibDiamond.sol (line 2)

pragma solidity ^0.8.7;

File: src/Libraries/LibAsset.sol (line 2)

pragma solidity ^0.8.7;

File: src/Libraries/LibStorage.sol (line 2)

pragma solidity ^0.8.7;

File: src/Interfaces/IAnyswapRouter.sol (line 2)

pragma solidity ^0.8.7;

File: src/Interfaces/IERC165.sol (line 2)

pragma solidity ^0.8.7;

File: src/Interfaces/IHopBridge.sol (line 2)

pragma solidity ^0.8.7;

File: src/Interfaces/IDiamondCut.sol (line 2)

pragma solidity ^0.8.7;

File: src/Interfaces/IDiamondLoupe.sol (line 2)

pragma solidity ^0.8.7;

File: src/Interfaces/ITransactionManager.sol (line 2)

pragma solidity 0.8.7;

File: src/Interfaces/IERC173.sol (line 2)

pragma solidity ^0.8.7;

File: src/Interfaces/IAnyswapToken.sol (line 2)

pragma solidity ^0.8.7;

File: src/Interfaces/ILiFi.sol (line 2)

pragma solidity ^0.8.7;

File: src/Interfaces/ICBridge.sol (line 2)

pragma solidity ^0.8.7;

File: src/LiFiDiamond.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/DexManagerFacet.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/NXTPFacet.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/OwnershipFacet.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/HopFacet.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/Swapper.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/GenericSwapFacet.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/DiamondCutFacet.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/WithdrawFacet.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/AnyswapFacet.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/DiamondLoupeFacet.sol (line 2)

pragma solidity ^0.8.7;

File: src/Facets/CBridgeFacet.sol (line 2)

pragma solidity ^0.8.7;

Splitting `require()` statements that use `&&` saves gas

See this issue for an example

File: src/Facets/Swapper.sol (lines 15-18)

            require(
                ls.dexWhitelist[_swapData[i].approveTo] == true && ls.dexWhitelist[_swapData[i].callTo] == true,
                "Contract call not allowed!"
            );

Duplicated `require()`/`revert()` checks should be refactored to a modifier or function

File: src/Libraries/LibDiamond.sol (line 102)

        require(_functionSelectors.length > 0, "LibDiamondCut: No selectors in facet to cut");

File: src/Libraries/LibDiamond.sol (line 104)

        require(_facetAddress != address(0), "LibDiamondCut: Add facet can't be address(0)");

File: src/Facets/AnyswapFacet.sol (line 105)

            require(_postSwapBalance > 0, "ERR_INVALID_AMOUNT");

File: src/Facets/CBridgeFacet.sol (line 116)

            require(_postSwapBalance > 0, "ERR_INVALID_AMOUNT");

Using `> 0` costs more gas than `!= 0` when used on a `uint` in a `require()` statement

File: src/Libraries/LibDiamond.sol (line 212)

        require(contractSize > 0, _errorMessage);

File: src/Facets/NXTPFacet.sol (line 98)

        require(_postSwapBalance > 0, "ERR_INVALID_AMOUNT");

File: src/Facets/HopFacet.sol (line 109)

        require(_postSwapBalance > 0, "ERR_INVALID_AMOUNT");

File: src/Facets/AnyswapFacet.sol (line 92)

            require(_postSwapBalance > 0, "ERR_INVALID_AMOUNT");

File: src/Facets/AnyswapFacet.sol (line 105)

            require(_postSwapBalance > 0, "ERR_INVALID_AMOUNT");

File: src/Facets/CBridgeFacet.sol (line 105)

            require(_postSwapBalance > 0, "ERR_INVALID_AMOUNT");

File: src/Facets/CBridgeFacet.sol (line 116)

            require(_postSwapBalance > 0, "ERR_INVALID_AMOUNT");

`require()`/`revert()` strings longer than 32 bytes cost extra gas

File: src/Libraries/LibDiamond.sol (line 56)

        require(msg.sender == diamondStorage().contractOwner, "LibDiamond: Must be contract owner");

File: src/Libraries/LibDiamond.sol (line 76)

                revert("LibDiamondCut: Incorrect FacetCutAction");

File: src/Libraries/LibDiamond.sol (line 84)

        require(_functionSelectors.length > 0, "LibDiamondCut: No selectors in facet to cut");

File: src/Libraries/LibDiamond.sol (line 86)

        require(_facetAddress != address(0), "LibDiamondCut: Add facet can't be address(0)");

File: src/Libraries/LibDiamond.sol (line 95)

            require(oldFacetAddress == address(0), "LibDiamondCut: Can't add function that already exists");

File: src/Libraries/LibDiamond.sol (line 102)

        require(_functionSelectors.length > 0, "LibDiamondCut: No selectors in facet to cut");

File: src/Libraries/LibDiamond.sol (line 104)

        require(_facetAddress != address(0), "LibDiamondCut: Add facet can't be address(0)");

File: src/Libraries/LibDiamond.sol (line 113)

            require(oldFacetAddress != _facetAddress, "LibDiamondCut: Can't replace function with same function");

File: src/Libraries/LibDiamond.sol (line 121)

        require(_functionSelectors.length > 0, "LibDiamondCut: No selectors in facet to cut");

File: src/Libraries/LibDiamond.sol (line 124)

        require(_facetAddress == address(0), "LibDiamondCut: Remove facet address must be address(0)");

File: src/Libraries/LibDiamond.sol (line 154)

        require(_facetAddress != address(0), "LibDiamondCut: Can't remove function that doesn't exist");

File: src/Libraries/LibDiamond.sol (line 156)

        require(_facetAddress != address(this), "LibDiamondCut: Can't remove immutable function");

File: src/Libraries/LibDiamond.sol (line 187)

            require(_calldata.length == 0, "LibDiamondCut: _init is address(0) but_calldata is not empty");

File: src/Libraries/LibDiamond.sol (line 189)

            require(_calldata.length > 0, "LibDiamondCut: _calldata is empty but _init is not address(0)");

File: src/Libraries/LibDiamond.sol (line 200)

                    revert("LibDiamondCut: _init function reverted");

File: src/Facets/HopFacet.sol (line 146)

        require(s.hopChainId != _hopData.chainId, "Cannot bridge to the same network.");

File: src/Facets/AnyswapFacet.sol (line 133)

        require(block.chainid != _anyswapData.toChainId, "Cannot bridge to the same network.");

File: src/Facets/CBridgeFacet.sol (line 147)

        require(s.cBridgeChainId != _cBridgeData.dstChainId, "Cannot bridge to the same network.");

State variables should be cached in stack variables rather than re-reading them from storage

The instances below point to the second access of a state variable within a function.
Less obvious optimizations include having local storage variables of mappings within state variable mappings or mappings within state variable structs, having local storage variables of structs within mappings, or having local caches of state variable contracts/addresses.

File: src/Facets/DexManagerFacet.sol (line 24)

        s.dexWhitelist[_dex] = true;

File: src/Facets/DexManagerFacet.sol (line 37)

            s.dexWhitelist[_dexs[i]] = true;

File: src/Facets/DexManagerFacet.sol (line 51)

        s.dexWhitelist[_dex] = false;

File: src/Facets/DexManagerFacet.sol (line 69)

            s.dexWhitelist[_dexs[i]] = false;

File: src/Facets/DexManagerFacet.sol (line 85)

        s.dexs[index] = s.dexs[s.dexs.length - 1];

File: src/Facets/Swapper.sol (line 16)

                ls.dexWhitelist[_swapData[i].approveTo] == true && ls.dexWhitelist[_swapData[i].callTo] == true,

Usage of `uints`/`ints` smaller than 32 bytes (256 bits) incurs overhead

When using elements that are smaller than 32 bytes, your contract’s gas usage may be higher. This is because the EVM operates on 32 bytes at a time. Therefore, if the element is smaller than that, the EVM must use more operations in order to reduce the size of the element from 32 bytes to the desired size.

https://docs.soliditylang.org/en/v0.8.11/internals/layout_in_storage.html
Use a larger size then downcast where needed

File: src/Libraries/LibDiamond.sol (line 11)

        uint96 functionSelectorPosition; // position in facetFunctionSelectors.functionSelectors array

File: src/Libraries/LibDiamond.sol (line 87)

        uint96 selectorPosition = uint96(ds.facetFunctionSelectors[_facetAddress].functionSelectors.length);

File: src/Libraries/LibDiamond.sol (line 105)

        uint96 selectorPosition = uint96(ds.facetFunctionSelectors[_facetAddress].functionSelectors.length);

File: src/Libraries/LibDiamond.sol (line 141)

        uint96 _selectorPosition,

File: src/Interfaces/ILiFi.sol (line 62)

    event Inited(address indexed bridge, uint64 chainId);

File: src/Interfaces/ICBridge.sol (line 9)

        uint64 _dstChinId,

File: src/Interfaces/ICBridge.sol (line 10)

        uint64 _nonce,

File: src/Interfaces/ICBridge.sol (line 11)

        uint32 _maxSlippage

File: src/Interfaces/ICBridge.sol (line 17)

        uint64 _dstChinId,

File: src/Interfaces/ICBridge.sol (line 18)

        uint64 _nonce,

File: src/Interfaces/ICBridge.sol (line 19)

        uint32 _maxSlippage

File: src/Facets/HopFacet.sol (line 48)

        for (uint8 i; i < _tokens.length; i++) {

File: src/Facets/Swapper.sol (line 14)

        for (uint8 i; i < _swapData.length; i++) {

File: src/Facets/CBridgeFacet.sol (line 21)

        uint64 cBridgeChainId;

File: src/Facets/CBridgeFacet.sol (line 30)

        uint64 dstChainId;

File: src/Facets/CBridgeFacet.sol (line 31)

        uint64 nonce;

File: src/Facets/CBridgeFacet.sol (line 32)

        uint32 maxSlippage;

File: src/Facets/CBridgeFacet.sol (line 42)

    function initCbridge(address _cBridge, uint64 _chainId) external {

Structs can be packed into fewer storage slots

File: src/Facets/CBridgeFacet.sol (lines 26-33)

    struct CBridgeData {
        address receiver;
        address token;
        uint256 amount;
        uint64 dstChainId;
        uint64 nonce;
        uint32 maxSlippage;
    }

Struct member ordering with 3 slots instead of the current 4:
uint256(32):amount,address(20):receiver,uint64(8):dstChainId,uint32(4):maxSlippage,address(20):token,uint64(8):nonce

Remove unused variables

File: src/Libraries/LibSwap.sol (line 8)

    uint256 private constant MAX_INT = 2**256 - 1;

Use custom error codes instead of revert strings to save gas

Various files and various locations

The text was updated successfully, but these errors were encountered:

H3xept · 2022-04-01T10:42:06Z

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

Fixed by lifinance/lifi-contracts@39dd074acf47b40f9a544439427e58de0208b961

H3xept · 2022-04-01T10:50:21Z

Re: ++i/i++ should be unchecked{++i}/unchecked{++i} when it is not possible for them to overflow, as is the case when used in for- and while-loops

We internally decided to avoid unchecked expressions for now.

H3xept · 2022-04-01T10:59:41Z

Re: Splitting require() statements that use && saves gas

I found no evidence online about this. Upon testing locally, this seems to be wrong (&& saves gas!!)

H3xept · 2022-04-01T11:01:12Z

Re: .length should not be looked up in every loop of a for-loop

Fixed by lifinance/lifi-contracts@975f12529f2232a59def392349bf8dccf4141aa9
Duplicate of #44

H3xept · 2022-04-01T11:03:56Z

Re: require()/revert() strings longer than 32 bytes cost extra gas

Fixed by lifinance/lifi-contracts@45edddfb56028db3cfd070b57990ae8a455f0109

H3xept · 2022-04-01T11:07:54Z

Re: State variables should be cached in stack variables rather than re-reading them from storage

Fixed by lifinance/lifi-contracts@2b0c057fb05c62d95c0b04edd1864c184ccf9ad8

H3xept · 2022-04-08T15:17:16Z

Re Unused variable MAX_INT

Duplicate of #100

H3xept · 2022-04-11T10:30:30Z

Re strings longer than 32 bytes cost extra gas

Duplicate of #100

H3xept · 2022-04-11T10:51:15Z

Re Structs can be packed into fewer storage slots

Duplicate of #178

H3xept · 2022-04-11T11:12:02Z

Re Using > 0 costs more gas than != 0 when used on a uint in a require() statement

Duplicate of #100

H3xept · 2022-04-11T12:02:00Z

Re prefix increments

We internally decided to avoid previx increments for now.

H3xept · 2022-04-11T12:41:49Z

Re calldata instead of memory for read-only arguments

Duplicate of #152

H3xept · 2022-04-11T12:52:46Z

Re pre-compute constant values

Duplicate of #182

code423n4 added bug Something isn't working G (Gas Optimization) labels Mar 30, 2022

code423n4 added a commit that referenced this issue Mar 30, 2022

IllIllI issue #196

42a625b

H3xept self-assigned this Apr 1, 2022

ezynda3 closed this as completed Apr 1, 2022

H3xept added the resolved Finding has been patched by sponsor (sponsor pls link to PR containing fix) label Apr 11, 2022

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Gas Optimizations #196

Gas Optimizations #196

code423n4 commented Mar 30, 2022

H3xept commented Apr 1, 2022

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H3xept commented Apr 1, 2022 •

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Gas Optimizations #196

Gas Optimizations #196

Comments

code423n4 commented Mar 30, 2022

Code refactoring

Don't compare boolean expressions to boolean literals

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

Superfluous event fields

++i/i++ should be unchecked{++i}/unchecked{++i} when it is not possible for them to overflow, as is the case when used in for- and while-loops

<array>.length should not be looked up in every loop of a for-loop

Using calldata instead of memory for read-only arguments in external functions saves gas

require() or revert() statements that check input arguments should be at the top of the function

internal functions only called once can be inlined to save gas

++i costs less gas than ++i, especially when it's used in for-loops (--i/i-- too)

Use a more recent version of solidity

Splitting require() statements that use && saves gas

Duplicated require()/revert() checks should be refactored to a modifier or function

Using > 0 costs more gas than != 0 when used on a uint in a require() statement

require()/revert() strings longer than 32 bytes cost extra gas

State variables should be cached in stack variables rather than re-reading them from storage

Usage of uints/ints smaller than 32 bytes (256 bits) incurs overhead

Structs can be packed into fewer storage slots

Remove unused variables

Use custom error codes instead of revert strings to save gas

H3xept commented Apr 1, 2022

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

H3xept commented Apr 1, 2022

Re: ++i/i++ should be unchecked{++i}/unchecked{++i} when it is not possible for them to overflow, as is the case when used in for- and while-loops

H3xept commented Apr 1, 2022

Re: Splitting require() statements that use && saves gas

H3xept commented Apr 1, 2022 • edited Loading

Re: .length should not be looked up in every loop of a for-loop

H3xept commented Apr 1, 2022

Re: require()/revert() strings longer than 32 bytes cost extra gas

H3xept commented Apr 1, 2022

Re: State variables should be cached in stack variables rather than re-reading them from storage

H3xept commented Apr 8, 2022

Re Unused variable MAX_INT

H3xept commented Apr 11, 2022

Re strings longer than 32 bytes cost extra gas

H3xept commented Apr 11, 2022

Re Structs can be packed into fewer storage slots

H3xept commented Apr 11, 2022

Re Using > 0 costs more gas than != 0 when used on a uint in a require() statement

H3xept commented Apr 11, 2022

Re prefix increments

H3xept commented Apr 11, 2022

Re calldata instead of memory for read-only arguments

H3xept commented Apr 11, 2022

Re pre-compute constant values

Expressions for constant values such as a call to `keccak256()`, should use `immutable` rather than `constant`

`++i`/`i++` should be `unchecked{++i}`/`unchecked{++i}` when it is not possible for them to overflow, as is the case when used in `for`- and `while`-loops

`<array>.length` should not be looked up in every loop of a `for`-loop

Using `calldata` instead of `memory` for read-only arguments in `external` functions saves gas

`require()` or `revert()` statements that check input arguments should be at the top of the function

`internal` functions only called once can be inlined to save gas

`++i` costs less gas than `++i`, especially when it's used in `for`-loops (`--i`/`i--` too)

Splitting `require()` statements that use `&&` saves gas

Duplicated `require()`/`revert()` checks should be refactored to a modifier or function

Using `> 0` costs more gas than `!= 0` when used on a `uint` in a `require()` statement

`require()`/`revert()` strings longer than 32 bytes cost extra gas

Usage of `uints`/`ints` smaller than 32 bytes (256 bits) incurs overhead

H3xept commented Apr 1, 2022 •

edited

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