ERC20SnapshotSolmate Code Style Findings

ERS-01C: Inefficient mapping Lookups

Type	Severity	Location
Gas Optimization		ERC20SnapshotSolmate.sol:L126, L129

Description:

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

Example:

Copy
119function transferFrom(
120    address from,
121    address to,
122    uint256 amount
123) public virtual returns (bool) {
124    _beforeTokenTransfer(from, to, amount);
125
126    uint256 allowed = allowance[from][msg.sender]; // Saves gas for limited approvals.
127
128    if (allowed != type(uint256).max)
129        allowance[from][msg.sender] = allowed - amount;
130
131    balanceOf[from] -= amount;
132
133    // Cannot overflow because the sum of all user
134    // balances can't exceed the max uint256 value.
135    unchecked {
136        balanceOf[to] += amount;
137    }
138
139    emit Transfer(from, to, amount);
140
141    return true;
142}

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.

Alleviation:

While the Pirex team acknowledges the gas optimization this change brings, they do not utilize the transferFrom function in their protocol and as such they will not apply the optimization in favor of code clarity.

ERS-02C: Variable Read Optimization

Type	Severity	Location
Gas Optimization		ERC20SnapshotSolmate.sol:L486, L489

Description:

The linked length variable is read twice from storage off the ids input argument.

Example:

Copy
481function _lastSnapshotId(uint256[] storage ids)
482    private
483    view
484    returns (uint256)
485{
486    if (ids.length == 0) {
487        return 0;
488    } else {
489        return ids[ids.length - 1];
490    }
491}

Recommendation:

We advise the ids.length lookup to be cached to a local variable instead optimizing the read-access gas cost of the function.

Alleviation:

The ids.length evaluation is now properly cached to an idsLen variable that is consequently utilized for the if clause and the array indice thereby optimizing the codebase.