#45309 [SC-Insight] Gas Optimization in `_burnForAtNow` Function for efficient balance retrieval

Submitted on May 12th 2025 at 13:18:46 UTC by @Bluedragon for Audit Comp | Flare | FAssets

• Report ID: #45309

• Report Type: Smart Contract

• Report severity: Insight

• Target: https://github.com/flare-labs-ltd/fassets/blob/main/docs/ImmunefiScope.md

• Impacts:

Description

Summary:

The _burnForAtNow function in the CheckPointable contract uses the balanceOfAt() function to retrieve the balance of an address at the current block. This approach is inefficient as balanceOfAt() internally calls valueAt(), which performs a binary search, leading to higher gas consumption. A more efficient alternative is to use a new function balanceOfNow() that leverages valueAtNow() to directly retrieve the latest checkpoint value.

Vulnerability Details:

• Root Cause: The use of balanceOfAt() for retrieving the current balance introduces unnecessary computational complexity due to the binary search performed by valueAt().

• Affected Function: _burnForAtNow

• File: contracts/fassetToken/implementation/CheckPointable.sol

• Technical Details: The valueAt() function performs a binary search to find the value at a specific block, which is unnecessary when retrieving the balance for the current block. The valueAtNow() function, which directly retrieves the last checkpoint value, can be used instead.

Impact:

• Increased gas costs for the _burnForAtNow function.

• Reduced efficiency of the contract, especially in scenarios with frequent token burns.

Recommended Mitigation:

Implement a new function balanceOfNow() in the CheckPointable contract:

function balanceOfNow(address _owner) public view returns (uint256 _balance) {
    return balanceHistory.valueAtNow(_owner);
}

Proof of Concept

Proof of Concept:

1. Call the _burnForAtNow function with a valid _owner and _amount.

2. Observe the gas usage due to the invocation of balanceOfAt() and its reliance on valueAt().