shw - Specification of the new base fee calculation is inconsistent with the code

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Specification of the new base fee calculation is inconsistent with the code

Summary

Specification of the new base fee calculation is inconsistent with the code.

Vulnerability Detail

The "Guaranteed Gas Fee Market" specification provides a pseudocode explaining how a new base fee is calculated, which has two inconsistencies with the actual code implementation:

1. When multiple blocks are skipped, the new base fee is applied with a 7/8 reduction per block. The code uses the updated newBaseFee (see ResourceMetering.sol#L115) while the specification uses the un-updated prev_basefee.
2. The maximum new base fee in the specification is UINT_64_MAX_VALUE but is set to type(uint128).max in the code.

Impact

The specification does not match the code.

Code Snippet

https://github.com/ethereum-optimism/optimism/blob/3f4b3c328153a8aa03611158b6984d624b17c1d9/packages/contracts-bedrock/contracts/L1/ResourceMetering.sol#L115

Tool used

Manual Review

Recommendation

Fix either the specification or the code.