Function compute_rbf 

pub(crate) fn compute_rbf(
    premium: &TokenAmount,
    replace_by_fee_ratio: Percent,
) -> TokenAmount

Computes the gas premium required to replace an existing message using provided replace-by-fee ratio.

See https://github.com/filecoin-project/lotus/blob/v1.36.0/chain/messagepool/messagepool.go#L215-L219