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chore: refactor L1BlockInfo::tx_estimated_size_fjord #1856

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chore: refactor L1BlockInfo::tx_estimated_size_fjord #1856

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4 changes: 3 additions & 1 deletion crates/optimism/src/fast_lz.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
/// Returns the length of the data after compression through FastLZ, based on
// https://github.com/Vectorized/solady/blob/5315d937d79b335c668896d7533ac603adac5315/js/solady.js
/// <https://github.com/Vectorized/solady/blob/5315d937d79b335c668896d7533ac603adac5315/js/solady.js>
/// The u32s match op-geth's Go port:
/// <https://github.com/ethereum-optimism/op-geth/blob/647c346e2bef36219cc7b47d76b1cb87e7ca29e4/core/types/rollup_cost.go#L411>
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pub(crate) fn flz_compress_len(input: &[u8]) -> u32 {
let mut idx: u32 = 2;

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24 changes: 18 additions & 6 deletions crates/optimism/src/l1block.rs
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Expand Up @@ -40,6 +40,16 @@ pub const BASE_FEE_RECIPIENT: Address = address!("420000000000000000000000000000
/// The address of the L1Block contract.
pub const L1_BLOCK_CONTRACT: Address = address!("4200000000000000000000000000000000000015");

/// <https://github.com/ethereum-optimism/op-geth/blob/647c346e2bef36219cc7b47d76b1cb87e7ca29e4/core/types/rollup_cost.go#L79>
const L1_COST_FASTLZ_COEF: u64 = 836_500;

/// <https://github.com/ethereum-optimism/op-geth/blob/647c346e2bef36219cc7b47d76b1cb87e7ca29e4/core/types/rollup_cost.go#L78>
/// Inverted to be used with `saturating_sub`.
const L1_COST_INTERCEPT: u64 = 42_585_600;

/// <https://github.com/ethereum-optimism/op-geth/blob/647c346e2bef36219cc7b47d76b1cb87e7ca29e4/core/types/rollup_cost.go#82>
const MIN_TX_SIZE_SCALED: u64 = 100 * 1_000_000;

/// L1 block info
///
/// We can extract L1 epoch data from each L2 block, by looking at the `setL1BlockValues`
Expand Down Expand Up @@ -161,12 +171,14 @@ impl L1BlockInfo {
// This value is computed based on the following formula:
// max(minTransactionSize, intercept + fastlzCoef*fastlzSize)
fn tx_estimated_size_fjord(&self, input: &[u8]) -> U256 {
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should we change this to u64?

looks like we use this in other places where we can also operate on u64

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@hai-rise hai-rise Nov 19, 2024 •
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The call in calculate_tx_l1_cost_fjord multiples with a large l1_fee_scaled so U256 is needed.

The call in data_gas looks pretty safe, but is not in any hot path as data_gas is only called in calculate_tx_l1_cost_bedrock and calculate_tx_l1_cost_ecotone that don't pass in a FJORD-enabled spec.

I'd say it's not worth it as it forces callers to mentally track u64::MAX to not wrap in a U256 anyway. It's easier within tx_estimated_size_fjord as we know even a u32::MAX returned by flz_compress_len wouldn't overflow u64.

let fastlz_size = U256::from(flz_compress_len(input));

fastlz_size
.saturating_mul(U256::from(836_500))
.saturating_sub(U256::from(42_585_600))
.max(U256::from(100_000_000))
let fastlz_size = flz_compress_len(input) as u64;

U256::from(
fastlz_size
.saturating_mul(L1_COST_FASTLZ_COEF)
.saturating_sub(L1_COST_INTERCEPT)
.max(MIN_TX_SIZE_SCALED),
)
}

/// Calculate the gas cost of a transaction based on L1 block data posted on L2, depending on the [OptimismSpecId] passed.
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