Gas optimization in XDEFIDistribution.sol - shifting instead of multiplying or dividing by power of 2

[code423n4]

Handle

OriDabush

Vulnerability details

XDEFIDistribution.sol lines 151, 338-344

Instead of multiplying by _pointsMultiplier, which is 2 ** 128, it is more efficient to shift by 128 (x * (2 ** 128) = x << 128), same for dividing (x / (2 ** 128) = x >> 128)

// line 151 - old
_pointsPerUnit += ((newXDEFI * _pointsMultiplier) / totalUnitsCached);

// line 151 - new
_pointsPerUnit += ((newXDEFI << 128) / totalUnitsCached);


// lines 338-344 - old
return
(
    _toUint256Safe(
        _toInt256Safe(_pointsPerUnit * uint256(units_)) +
        pointsCorrection_
    ) / _pointsMultiplier
) + uint256(depositedXDEFI_);

// lines 338-344 - new
return
(
    _toUint256Safe(
        _toInt256Safe(_pointsPerUnit * uint256(units_)) +
        pointsCorrection_
    ) >> 128
) + uint256(depositedXDEFI_);

[deluca-mike]

Yup, this is valid. Will do.

[deluca-mike]

In release candidate contract, _pointsMultiplier (now POINTS_MULTIPLIER_BITS) is defined as a number of bits to shift, and shifting is occuring (instead of multiplication) in updateDistribution, and instead of division in _withdrawableGiven.

[Ivshti]

that's a good one!