Submission Details
Severity:
Multiple Address Mappings Can Be Combined Into A Single Mapping Of An Address To A Struct, Where Appropriate
Vulnerability Details
Saves a storage slot for the mapping. Depending on the circumstances and sizes of types, can avoid a Gsset (20000 gas) per mapping combined. Reads and subsequent writes can also be cheaper when a function requires both values and they both fit in the same storage slot.
Finally, if both fields are accessed in the same function, can save ~42 gas per access due to not having to recalculate the key’s keccak256 hash (Gkeccak256 - 30 gas) and that calculation’s associated stack operations.
Proof of Concept
File: src/DSCEngine.sol
77: mapping(address token => address priceFeed) private s_priceFeeds; // tokenToPriceFeed
78: mapping(address user => mapping(address token => uint256 amount)) private s_collateralDeposited;
79: mapping(address user => uint256 amountDscMinted) private s_DSCMinted;
Tools Used
VSCode
Prize pool breakdown
Total prize
15,000 USDC
nSLOC
23664 USDC / LOC
14,000 USDC
1,000 USDC
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