[EHF-01C] Inefficient mapping Lookups

[zajck]

EHF-01C: Inefficient mapping Lookups

Type	Severity	Location
Gas Optimization		ExchangeHandlerFacet.sol:L993, L1001, L1005, L1013

Description:

The linked statements perform key-based lookup operations on mapping declarations from storage multiple times for the same key redundantly.

Example:

if (_condition.method == EvaluationMethod.SpecificToken) {
    // How many times has this token id been used to commit to offers in the group?
    uint256 commitCount = lookups.conditionalCommitsByTokenId[_tokenId][_groupId];

    require(commitCount < _condition.maxCommits, MAX_COMMITS_TOKEN_REACHED);

    allow = holdsSpecificToken(_buyer, _condition, _tokenId);

    if (allow) {
        // Increment number of commits to the group for this token id if they are allowed to commit
        lookups.conditionalCommitsByTokenId[_tokenId][_groupId] = ++commitCount;
    }
} else if (_condition.method == EvaluationMethod.Threshold) {
    // How many times has this address committed to offers in the group?
    uint256 commitCount = lookups.conditionalCommitsByAddress[_buyer][_groupId];

    require(commitCount < _condition.maxCommits, MAX_COMMITS_ADDRESS_REACHED);

    allow = holdsThreshold(_buyer, _condition, _tokenId);

    if (allow) {
        // Increment number of commits to the group for this address if they are allowed to commit
        lookups.conditionalCommitsByAddress[_buyer][_groupId] = ++commitCount;
    }
} else {

Recommendation:

As the lookups internally perform an expensive keccak256 operation, we advise the lookups to be cached wherever possible to a single local declaration that either holds the value of the mapping in case of primitive types or holds a storage pointer to the struct contained.