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fix: Outbox replay state management, saves ~15k gas per msg #623

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Merged
PlasmaPower merged 11 commits into from
Jun 15, 2022
Merged

fix: Outbox replay state management, saves ~15k gas per msg #623

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d811bcf
feat: ~20k gas saving per msg w packed bitmap
shotaronowhere May 18, 2022
738e2a6
Merge branch 'OffchainLabs:master' into master
shotaronowhere May 18, 2022
6abed39
Merge branch 'OffchainLabs:master' into master
shotaronowhere May 24, 2022
3361350
feat: Reserve the MSB of the spent bitmap.
shotaronowhere May 24, 2022
a83d50e
Merge branch 'master' into master
hkalodner Jun 3, 2022
b0478de
Merge branch 'master' into master
fredlacs Jun 7, 2022
895f7a5
Merge branch 'master' into master
hkalodner Jun 7, 2022
cebded4
Merge branch 'master' into master
PlasmaPower Jun 14, 2022
def5990
Merge branch 'master' into master
PlasmaPower Jun 14, 2022
3f7684f
feat(replay): gas optimization
shotaronowhere Jun 14, 2022
31b7910
Merge branch 'master' into master
PlasmaPower Jun 15, 2022
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10 changes: 7 additions & 3 deletions contracts/src/bridge/Outbox.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ contract Outbox is DelegateCallAware, IOutbox {
address public rollup; // the rollup contract
IBridge public bridge; // the bridge contract

mapping(uint256 => bool) public spent; // maps leaf number => if spent
mapping(uint256 => bytes32) public spent; // packed spent bitmap
mapping(bytes32 => bytes32) public roots; // maps root hashes => L2 block hash

struct L2ToL1Context {
Expand Down Expand Up @@ -182,8 +182,12 @@ contract Outbox is DelegateCallAware, IOutbox {
bytes32 calcRoot = calculateMerkleRoot(proof, index, item);
if (roots[calcRoot] == bytes32(0)) revert UnknownRoot(calcRoot);

if (spent[index]) revert AlreadySpent(index);
spent[index] = true;
uint256 spentIndex = index / 256;
uint256 bitOffset = index - spentIndex * 256;

@tsahee tsahee May 24, 2022

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Let's use 255 instead of 256 here.. this will leave the most significant bit reserved.
We might do something clever with this reserved bit later, to avoid 1/256 users paying more gas for the release.

@shotaronowhere shotaronowhere May 24, 2022

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Sure, just made that change. : )


bytes32 replay = spent[spentIndex];
if (((replay >> bitOffset) & bytes32(uint256(1))) != bytes32(0)) revert AlreadySpent(index);
spent[spentIndex] = (replay | bytes32(1 << bitOffset));

return bytes32(index);
}
Expand Down