reth/crates/primitives/src/basefee.rs

//! Helpers for working with EIP-1559 base fee

/// Calculate the base fee for the next block based on the EIP-1559 specification.
///
/// This function calculates the base fee for the next block according to the rules defined in the
/// EIP-1559. EIP-1559 introduces a new transaction pricing mechanism that includes a
/// fixed-per-block network fee that is burned and dynamically adjusts block sizes to handle
/// transient congestion.
///
/// For each block, the base fee per gas is determined by the gas used in the parent block and the
/// target gas (the block gas limit divided by the elasticity multiplier). The algorithm increases
/// the base fee when blocks are congested and decreases it when they are under the target gas
/// usage. The base fee per gas is always burned.
///
/// Parameters:
/// - `gas_used`: The gas used in the current block.
/// - `gas_limit`: The gas limit of the current block.
/// - `base_fee`: The current base fee per gas.
/// - `base_fee_params`: Base fee parameters such as elasticity multiplier and max change
///   denominator.
///
/// Returns:
/// The calculated base fee for the next block as a `u64`.
///
/// For more information, refer to the [EIP-1559 spec](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1559.md).
pub fn calculate_next_block_base_fee(
    gas_used: u64,
    gas_limit: u64,
    base_fee: u64,
    base_fee_params: crate::BaseFeeParams,
) -> u64 {
    // Calculate the target gas by dividing the gas limit by the elasticity multiplier.
    let gas_target = gas_limit / base_fee_params.elasticity_multiplier;

    match gas_used.cmp(&gas_target) {
        // If the gas used in the current block is equal to the gas target, the base fee remains the
        // same (no increase).
        std::cmp::Ordering::Equal => base_fee,
        // If the gas used in the current block is greater than the gas target, calculate a new
        // increased base fee.
        std::cmp::Ordering::Greater => {
            // Calculate the increase in base fee based on the formula defined by EIP-1559.
            base_fee +
                (std::cmp::max(
                    // Ensure a minimum increase of 1.
                    1,
                    base_fee as u128 * (gas_used - gas_target) as u128 /
                        (gas_target as u128 * base_fee_params.max_change_denominator as u128),
                ) as u64)
        }
        // If the gas used in the current block is less than the gas target, calculate a new
        // decreased base fee.
        std::cmp::Ordering::Less => {
            // Calculate the decrease in base fee based on the formula defined by EIP-1559.
            base_fee.saturating_sub(
                (base_fee as u128 * (gas_target - gas_used) as u128 /
                    (gas_target as u128 * base_fee_params.max_change_denominator as u128))
                    as u64,
            )
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn calculate_base_fee_success() {
        let base_fee = [
            1000000000, 1000000000, 1000000000, 1072671875, 1059263476, 1049238967, 1049238967, 0,
            1, 2,
        ];
        let gas_used = [
            10000000, 10000000, 10000000, 9000000, 10001000, 0, 10000000, 10000000, 10000000,
            10000000,
        ];
        let gas_limit = [
            10000000, 12000000, 14000000, 10000000, 14000000, 2000000, 18000000, 18000000,
            18000000, 18000000,
        ];
        let next_base_fee = [
            1125000000, 1083333333, 1053571428, 1179939062, 1116028649, 918084097, 1063811730, 1,
            2, 3,
        ];

        for i in 0..base_fee.len() {
            assert_eq!(
                next_base_fee[i],
                calculate_next_block_base_fee(
                    gas_used[i],
                    gas_limit[i],
                    base_fee[i],
                    crate::BaseFeeParams::ethereum(),
                )
            );
        }
    }

    #[cfg(feature = "optimism")]
    #[test]
    fn calculate_optimism_base_fee_success() {
        let base_fee = [
            1000000000, 1000000000, 1000000000, 1072671875, 1059263476, 1049238967, 1049238967, 0,
            1, 2,
        ];
        let gas_used = [
            10000000, 10000000, 10000000, 9000000, 10001000, 0, 10000000, 10000000, 10000000,
            10000000,
        ];
        let gas_limit = [
            10000000, 12000000, 14000000, 10000000, 14000000, 2000000, 18000000, 18000000,
            18000000, 18000000,
        ];
        let next_base_fee = [
            1100000048, 1080000000, 1065714297, 1167067046, 1128881311, 1028254188, 1098203452, 1,
            2, 3,
        ];

        for i in 0..base_fee.len() {
            assert_eq!(
                next_base_fee[i],
                calculate_next_block_base_fee(
                    gas_used[i],
                    gas_limit[i],
                    base_fee[i],
                    crate::BaseFeeParams::optimism(),
                )
            );
        }
    }

    #[cfg(feature = "optimism")]
    #[test]
    fn calculate_optimism_sepolia_base_fee_success() {
        let base_fee = [
            1000000000, 1000000000, 1000000000, 1072671875, 1059263476, 1049238967, 1049238967, 0,
            1, 2,
        ];
        let gas_used = [
            10000000, 10000000, 10000000, 9000000, 10001000, 0, 10000000, 10000000, 10000000,
            10000000,
        ];
        let gas_limit = [
            10000000, 12000000, 14000000, 10000000, 14000000, 2000000, 18000000, 18000000,
            18000000, 18000000,
        ];
        let next_base_fee = [
            1180000000, 1146666666, 1122857142, 1244299375, 1189416692, 1028254188, 1144836295, 1,
            2, 3,
        ];

        for i in 0..base_fee.len() {
            assert_eq!(
                next_base_fee[i],
                calculate_next_block_base_fee(
                    gas_used[i],
                    gas_limit[i],
                    base_fee[i],
                    crate::BaseFeeParams::optimism_sepolia(),
                )
            );
        }
    }
}