MovingAverage.sol#_getFirstSample() Implementation can be simpler and save some gas

[code423n4]

Handle

WatchPug

Vulnerability details

https://github.com/code-423n4/2021-11-malt/blob/c3a204a2c0f7c653c6c2dda9f4563fd1dc1cecf3/src/contracts/MovingAverage.sol#L362-L367

  function _getFirstSample() private view returns (Sample storage firstSample) {
    uint32 sampleIndex = _getIndexOfSample(counter);
    // no overflow issue. if sampleIndex + 1 overflows, result is still zero.
    uint32 firstSampleIndex = uint32((sampleIndex + 1) % sampleMemory);
    firstSample = samples[firstSampleIndex];
  }

Recommendation

Change to:

  function _getFirstSample() private view returns (Sample storage firstSample) {
    // no overflow issue. if sampleIndex + 1 overflows, result is still zero.
    firstSample = samples[(counter + 1) % sampleMemory];
  }

[0xScotch]

#252 points out an issue with the logic and will be fixed accordingly.

[GalloDaSballo]

In principle I agree with the finding and believe it would save gas. Not super sure if this addresses the other concerns other wardens raised