gas: add unchecked for ConduitController#updateChannel #440
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`channelPreviouslyOpen` is `true` means that `channelIndexPlusOne != 0`, and `channelIndexPlusOne` is `uint256`, then `channelIndexPlusOne - 1` will never underflow.
ryanio
reviewed
Jun 8, 2022
Co-authored-by: Ryan Ghods <[email protected]>
leonardoalt
reviewed
Jun 8, 2022
| uint256 removedChannelIndex; | ||
| // channelPreviouslyOpen already ensures channelIndexPlusOne > 0 | ||
| unchecked { | ||
| removedChannelIndex = channelIndexPlusOne - 1; |
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To clarify: this is safe.
In this branch, channelPreviouslyOpen must be true, which means that channelIndexPlusOne != 0. Since it has type uint, it must be > 0 therefore safe.
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Motivation
For the arithmetic operations that will never over/underflow, using the unchecked directive (Solidity v0.8 has default overflow/underflow checks) can save some gas from the unnecessary internal over/underflow checks.
In
ConduitController.sol#updateChannel(), whenchannelPreviouslyOpenistruemeans thatchannelIndexPlusOne != 0, andchannelIndexPlusOneisuint256, sochannelIndexPlusOnemust >= 1, thenchannelIndexPlusOne - 1will never underflow.Solution
add
uncheckedfor that case