diff --git a/prdoc/pr_3636.prdoc b/prdoc/pr_3636.prdoc new file mode 100644 index 000000000000..934158ac1022 --- /dev/null +++ b/prdoc/pr_3636.prdoc @@ -0,0 +1,15 @@ +# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0 +# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json + +title: "[pallet_broker] Fix `Linear::adapt_price` behavior at zero" + +doc: + - audience: Runtime Dev + description: | + This fixes the behaviour of `Linear` which is the default implementation of the `AdaptPrice` + trait in the broker pallet. Previously if cores were offered but not sold in only one sale, + the price would be set to zero and due to the logic being purely multiplicative, the price + would stay at 0 indefinitely. + +crates: + - name: pallet-broker diff --git a/substrate/frame/broker/src/adapt_price.rs b/substrate/frame/broker/src/adapt_price.rs index 8266625687a2..fbcd7afdf0da 100644 --- a/substrate/frame/broker/src/adapt_price.rs +++ b/substrate/frame/broker/src/adapt_price.rs @@ -19,6 +19,7 @@ use crate::CoreIndex; use sp_arithmetic::{traits::One, FixedU64}; +use sp_runtime::Saturating; /// Type for determining how to set price. pub trait AdaptPrice { @@ -49,14 +50,24 @@ impl AdaptPrice for () { pub struct Linear; impl AdaptPrice for Linear { fn leadin_factor_at(when: FixedU64) -> FixedU64 { - FixedU64::from(2) - when + FixedU64::from(2).saturating_sub(when) } fn adapt_price(sold: CoreIndex, target: CoreIndex, limit: CoreIndex) -> FixedU64 { if sold <= target { - FixedU64::from_rational(sold.into(), target.into()) + // Range of [0.5, 1.0]. + FixedU64::from_rational(1, 2).saturating_add(FixedU64::from_rational( + sold.into(), + target.saturating_mul(2).into(), + )) } else { - FixedU64::one() + - FixedU64::from_rational((sold - target).into(), (limit - target).into()) + // Range of (1.0, 2]. + + // Unchecked math: In this branch we know that sold > target. The limit must be >= sold + // by construction, and thus target must be < limit. + FixedU64::one().saturating_add(FixedU64::from_rational( + (sold - target).into(), + (limit - target).into(), + )) } } } @@ -81,4 +92,23 @@ mod tests { } } } + + #[test] + fn linear_bound_check() { + // Using constraints from pallet implementation i.e. `limit >= sold`. + // Check extremes + let limit = 10; + let target = 5; + + // Maximally sold: `sold == limit` + assert_eq!(Linear::adapt_price(limit, target, limit), FixedU64::from_float(2.0)); + // Ideally sold: `sold == target` + assert_eq!(Linear::adapt_price(target, target, limit), FixedU64::one()); + // Minimally sold: `sold == 0` + assert_eq!(Linear::adapt_price(0, target, limit), FixedU64::from_float(0.5)); + // Optimistic target: `target == limit` + assert_eq!(Linear::adapt_price(limit, limit, limit), FixedU64::one()); + // Pessimistic target: `target == 0` + assert_eq!(Linear::adapt_price(limit, 0, limit), FixedU64::from_float(2.0)); + } }