MerkleDistributor Code Style Findings

MDR-01C: Redundant Visibility Specifier

Description:

The linked variable is meant to be an internally accessible constant yet is declared as public.

Example:

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10address public immutable override token;
11bytes32 public immutable override merkleRoot;
12uint256 public claimPeriodEndBlock;
13uint256 public constant CLAIM_PERIOD_BLOCKS = 17280 * 365;

Recommendation:

We advise the public specifier to be replaced by either an internal or private one given the variable has no use outside of the contract and can be represented by its literal form.

Alleviation:

The variable is now properly set as private.

MDR-02C: Statement Inefficiency

Description:

The claim function first validates that a particular index has not been claimed and then proceeds to claim it, however, in doing so it performs multiple storage reads and memory writes redundantly twice.

Example:

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37function isClaimed(uint256 index) public view override returns (bool) {
38    uint256 claimedWordIndex = index / 256;
39    uint256 claimedBitIndex = index % 256;
40    uint256 claimedWord = claimedBitMap[claimedWordIndex];
41    uint256 mask = (1 << claimedBitIndex);
42    return claimedWord & mask == mask;
43}
44
45function _setClaimed(uint256 index) private {
46    uint256 claimedWordIndex = index / 256;
47    uint256 claimedBitIndex = index % 256;
48    claimedBitMap[claimedWordIndex] = claimedBitMap[claimedWordIndex] | (1 << claimedBitIndex);
49}

Recommendation:

We advise the _setClaimed function to be adjusted to yield a bool if the bit map has not already been claimed and the function should be directly used within the require statement that isClaimed previously was. The isClaimed function should still exist for off-chain purposes, however, the on-chain component should strive for maximal gas efficiency.

Alleviation:

The _setClaimed code has been optimised as per our recommendation and now properly yields a bool indicating its success.