implement muldiv without overflow and underflow

Signed-off-by: Uncle Stretch <uncle.stretch@ghostchain.io>

Cargo.lock

@@ -3649,13 +3649,14 @@ dependencies = [
 
 [[package]]
 name = "ghost-networks"
-version = "0.1.13"
+version = "0.1.14"
 dependencies = [
  "frame-benchmarking",
  "frame-support",
  "frame-system",
  "ghost-core-primitives",
  "ghost-traits",
+ "num-traits",
  "pallet-balances",
  "pallet-staking",
  "pallet-staking-reward-curve",

Cargo.toml

@@ -69,6 +69,7 @@ bs58 = { version = "0.5.0" }
 prometheus-parse = { version = "0.2.2" }
 rustc-hex = { version = "2.1.0", default-features = false }
 log = { version = "0.4", default-features = false }
+num-traits = { version = "0.2.17", default-features = false }
 libsecp256k1 = { version = "0.7", default-features = false }
 bip39 = { package = "parity-bip39", version = "2.0.1" }
 sha3 = { version = "0.10", default-features = false }

pallets/networks/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ghost-networks"
-version = "0.1.13"
+version = "0.1.14"
 license.workspace = true
 authors.workspace = true
 edition.workspace = true
@@ -10,6 +10,7 @@ repository.workspace = true
 [dependencies]
 scale-info = { workspace = true, features = ["derive"] }
 codec = { workspace = true, features = ["max-encoded-len"] }
+num-traits = { workspace = true }
 
 frame-benchmarking = { workspace = true, optional = true }
 frame-support = { workspace = true }
@@ -30,6 +31,7 @@ default = ["std"]
 std = [
     "scale-info/std",
     "codec/std",
+    "num-traits/std",
     "frame-support/std",
     "frame-system/std",
     "frame-benchmarking?/std",

pallets/networks/src/lib.rs

@@ -21,9 +21,11 @@ pub use ghost_traits::networks::{
     NetworkDataBasicHandler, NetworkDataInspectHandler, NetworkDataMutateHandler,
 };
 
+mod math;
 mod weights;
 
 pub use crate::weights::WeightInfo;
+use math::MulDiv;
 pub use module::*;
 
 #[cfg(any(feature = "runtime-benchmarks", test))]
@@ -73,7 +75,15 @@ pub struct BridgedInflationCurve<RewardCurve, T>(core::marker::PhantomData<(Rewa
 impl<Balance, RewardCurve, T> pallet_staking::EraPayout<Balance>
     for BridgedInflationCurve<RewardCurve, T>
 where
-    Balance: Default + AtLeast32BitUnsigned + Clone + Copy + From<u128>,
+    Balance: Default
+        + Copy
+        + From<BalanceOf<T>>
+        + AtLeast32BitUnsigned
+        + num_traits::ops::wrapping::WrappingAdd
+        + num_traits::ops::overflowing::OverflowingAdd
+        + sp_std::ops::AddAssign
+        + sp_std::ops::Not<Output = Balance>
+        + sp_std::ops::BitAnd<u128, Output = Balance>,
     RewardCurve: Get<&'static PiecewiseLinear<'static>>,
     T: Config,
 {
@@ -82,30 +92,27 @@ where
         total_issuance: Balance,
         _era_duration_in_millis: u64,
     ) -> (Balance, Balance) {
-        let piecewise_linear = RewardCurve::get();
-        let bridge_adjustment = BridgedImbalance::<T>::get();
+        let reward_curve = RewardCurve::get();
+        let bridged_imbalance = BridgedImbalance::<T>::get();
         let accumulated_commission = AccumulatedCommission::<T>::get();
 
-        let bridged_out: u128 = bridge_adjustment.bridged_out.try_into().unwrap_or_default();
-        let bridged_in: u128 = bridge_adjustment.bridged_in.try_into().unwrap_or_default();
-        let accumulated_commission: u128 = accumulated_commission.try_into().unwrap_or_default();
-
-        let accumulated_balance = Balance::from(accumulated_commission);
-        let adjusted_issuance = match bridged_out > bridged_in {
-            true => total_issuance.saturating_add(Balance::from(bridged_out - bridged_in)),
-            false => total_issuance.saturating_sub(Balance::from(bridged_in - bridged_out)),
-        };
+        let accumulated_commission: Balance = accumulated_commission.into();
+        let adjusted_issuance: Balance = total_issuance
+            .saturating_add(bridged_imbalance.bridged_out.into())
+            .saturating_sub(bridged_imbalance.bridged_in.into());
 
         NullifyNeeded::<T>::set(true);
 
-        match piecewise_linear
-            .calculate_for_fraction_times_denominator(total_staked, adjusted_issuance)
-            .checked_mul(&accumulated_balance)
-            .and_then(|product| product.checked_div(&adjusted_issuance))
-        {
-            Some(payout) => (payout, accumulated_balance.saturating_sub(payout)),
-            None => (Balance::default(), Balance::default()),
-        }
+        let estimated_reward =
+            reward_curve.calculate_for_fraction_times_denominator(total_staked, adjusted_issuance);
+        let payout = MulDiv::<Balance>::calculate(
+            estimated_reward,
+            accumulated_commission,
+            adjusted_issuance,
+        );
+        let rest_payout = accumulated_commission.saturating_sub(payout);
+
+        (payout, rest_payout)
     }
 }
 

pallets/networks/src/math.rs

@@ -0,0 +1,120 @@
+use crate::AtLeast32BitUnsigned;
+
+pub struct MulDiv<Balance>(core::marker::PhantomData<Balance>);
+impl<Balance> MulDiv<Balance>
+where
+    Balance: Copy
+        + AtLeast32BitUnsigned
+        + num_traits::ops::wrapping::WrappingAdd
+        + num_traits::ops::overflowing::OverflowingAdd
+        + sp_std::ops::AddAssign
+        + sp_std::ops::Not<Output = Balance>
+        + sp_std::ops::BitAnd<u128, Output = Balance>,
+{
+    fn least_significant_bits(&self, a: Balance) -> Balance {
+        a & ((1 << 64) - 1)
+    }
+
+    fn most_significant_bits(&self, a: Balance) -> Balance {
+        a >> 64
+    }
+
+    fn two_complement(&self, a: Balance) -> Balance {
+        let one: Balance = 1u32.into();
+        (!a).wrapping_add(&one)
+    }
+
+    fn adjusted_ratio(&self, a: Balance) -> Balance {
+        let one: Balance = 1u32.into();
+        (self.two_complement(a) / a).wrapping_add(&one)
+    }
+
+    fn modulo(&self, a: Balance) -> Balance {
+        self.two_complement(a) % a
+    }
+
+    fn overflow_resistant_addition(
+        &self,
+        a0: Balance,
+        a1: Balance,
+        b0: Balance,
+        b1: Balance,
+    ) -> (Balance, Balance) {
+        let (r0, overflow) = a0.overflowing_add(&b0);
+        let overflow: Balance = overflow.then(|| 1u32).unwrap_or_default().into();
+        let r1 = a1.wrapping_add(&b1).wrapping_add(&overflow);
+        (r0, r1)
+    }
+
+    fn overflow_resistant_multiplication(&self, a: Balance, b: Balance) -> (Balance, Balance) {
+        let (a0, a1) = (
+            self.least_significant_bits(a),
+            self.most_significant_bits(a),
+        );
+        let (b0, b1) = (
+            self.least_significant_bits(b),
+            self.most_significant_bits(b),
+        );
+        let (x, y) = (a1 * b0, b1 * a0);
+
+        let (r0, r1) = (a0 * b0, a1 * b1);
+        let (r0, r1) = self.overflow_resistant_addition(
+            r0,
+            r1,
+            self.least_significant_bits(x) << 64,
+            self.most_significant_bits(x),
+        );
+        let (r0, r1) = self.overflow_resistant_addition(
+            r0,
+            r1,
+            self.least_significant_bits(y) << 64,
+            self.most_significant_bits(y),
+        );
+
+        (r0, r1)
+    }
+
+    fn overflow_resistant_division(
+        &self,
+        mut a0: Balance,
+        mut a1: Balance,
+        b: Balance,
+    ) -> (Balance, Balance) {
+        if b == 1u32.into() {
+            return (a0, a1);
+        }
+
+        let zero: Balance = 0u32.into();
+        let (q, r) = (self.adjusted_ratio(b), self.modulo(b));
+        let (mut x0, mut x1) = (zero, zero);
+
+        while a1 != zero {
+            let (t0, t1) = self.overflow_resistant_multiplication(a1, q);
+            let (new_x0, new_x1) = self.overflow_resistant_addition(x0, x1, t0, t1);
+            x0 = new_x0;
+            x1 = new_x1;
+
+            let (t0, t1) = self.overflow_resistant_multiplication(a1, r);
+            let (new_a0, new_a1) = self.overflow_resistant_addition(t0, t1, a0, zero);
+            a0 = new_a0;
+            a1 = new_a1;
+        }
+
+        self.overflow_resistant_addition(x0, x1, a0 / b, zero)
+    }
+
+    fn mul_div(&self, a: Balance, b: Balance, c: Balance) -> Balance {
+        let (t0, t1) = self.overflow_resistant_multiplication(a, b);
+        self.overflow_resistant_division(t0, t1, c).0
+    }
+
+    pub fn calculate(a: Balance, b: Balance, c: Balance) -> Balance {
+        let zero: Balance = 0u32.into();
+        if a == zero || b == zero || c == zero {
+            return zero;
+        }
+
+        let inner = MulDiv(core::marker::PhantomData);
+        inner.mul_div(a, b, c)
+    }
+}

pallets/networks/src/tests.rs

@@ -1295,8 +1295,10 @@ fn accumulated_commission_could_be_nullified() {
 #[test]
 fn bridged_inlation_reward_works() {
     ExtBuilder::build().execute_with(|| {
-        let amount: u128 = 1337 * 1_000_000_000;
-        let commission: u128 = amount / 100; // 1% commission
+        let amount_full: u128 = 1337 * 1_000_000_000;
+        let commission: u128 = amount_full / 100; // 1% commission
+        let amount: u128 = amount_full - commission;
+
         let total_staked_ideal: u128 = 69;
         let total_staked_not_ideal: u128 = 68;
         let total_issuance: u128 = 100;
@@ -1538,8 +1540,10 @@ fn bridged_inlation_reward_works() {
 #[test]
 fn bridged_inflation_era_payout_triggers_need_of_nullification() {
     ExtBuilder::build().execute_with(|| {
-        let amount: u128 = 1337 * 1_000_000_000;
-        let commission: u128 = amount / 100; // 1% commission
+        let amount_full: u128 = 1337 * 1_000_000_000;
+        let commission: u128 = amount_full / 100; // 1% commission
+        let amount: u128 = amount_full - commission;
+
         let total_staked_ideal: u128 = 69;
         let total_issuance: u128 = 100;
 
@@ -1570,3 +1574,165 @@ fn trigger_nullification_works_as_expected() {
         assert_eq!(NullifyNeeded::<Test>::get(), false);
     });
 }
+
+#[test]
+fn check_substrate_guarantees_not_to_overflow() {
+    ExtBuilder::build().execute_with(|| {
+        let reward_curve = RewardCurve::get();
+        let mut n: u128 = 69;
+        let mut d: u128 = 100;
+
+        loop {
+            n = match n.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+            d = match d.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+            assert_eq!(
+                reward_curve.calculate_for_fraction_times_denominator(n, d),
+                d
+            );
+        }
+    });
+}
+
+#[test]
+fn check_muldiv_guarantees_not_to_overflow() {
+    ExtBuilder::build().execute_with(|| {
+        let mut a: u128 = 2;
+        let mut b: u128 = 3;
+        let mut c: u128 = 6;
+        let mut result: u128 = 1;
+
+        loop {
+            a = match a.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+            b = match b.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+            c = match c.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+            result = match result.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+
+            assert_eq!(MulDiv::<u128>::calculate(a, b, c), result);
+        }
+
+        assert_eq!(
+            MulDiv::<u128>::calculate(u128::MAX, u128::MAX, u128::MAX),
+            u128::MAX
+        );
+        assert_eq!(MulDiv::<u128>::calculate(u128::MAX, 0, 0), 0);
+        assert_eq!(MulDiv::<u128>::calculate(0, u128::MAX, 0), 0);
+        assert_eq!(MulDiv::<u128>::calculate(0, 0, u128::MAX), 0);
+    });
+}
+
+#[test]
+fn check_bridged_inflation_curve_for_overflow() {
+    ExtBuilder::build().execute_with(|| {
+        let amount_full: u128 = 1337 * 1_000_000_000;
+        let commission: u128 = amount_full / 100; // 1% commission
+        let amount: u128 = amount_full - commission;
+
+        let tollerance: u128 = commission / 100; // 1% tollerance
+        let precomputed_payout: u128 = 13177568884;
+        let precomputed_rest: u128 = 192431116;
+        assert_eq!(precomputed_payout + precomputed_rest, commission);
+
+        let mut total_staked_ideal: u128 = 69_000;
+        let mut total_staked_not_ideal: u128 = 68_000;
+        let mut total_issuance: u128 = 100_000;
+
+        assert_ok!(GhostNetworks::accumulate_commission(&commission));
+        assert_ok!(GhostNetworks::accumulate_incoming_imbalance(&amount));
+
+        loop {
+            total_staked_ideal = match total_staked_ideal.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+            total_staked_not_ideal = match total_staked_not_ideal.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+            total_issuance = match total_issuance.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+            assert_eq!(
+                BridgedInflationCurve::<RewardCurve, Test>::era_payout(
+                    total_staked_ideal,
+                    total_issuance + amount,
+                    0
+                ),
+                (commission, 0)
+            );
+
+            let (payout, rest) = BridgedInflationCurve::<RewardCurve, Test>::era_payout(
+                total_staked_not_ideal,
+                total_issuance + amount,
+                0,
+            );
+
+            let payout_deviation = if precomputed_payout > payout {
+                precomputed_payout - payout
+            } else {
+                payout - precomputed_payout
+            };
+
+            let rest_deviation = if precomputed_rest > rest {
+                precomputed_rest - rest
+            } else {
+                rest - precomputed_rest
+            };
+
+            assert!(payout_deviation < tollerance);
+            assert!(rest_deviation < tollerance);
+        }
+    });
+}
+
+#[test]
+fn check_bridged_inflation_curve_for_big_commissions() {
+    ExtBuilder::build().execute_with(|| {
+        let mut amount_full: u128 = 1337;
+
+        let total_staked_ideal: u128 = 69_000_000;
+        let total_issuance: u128 = 100_000_000;
+
+        loop {
+            amount_full = match amount_full.checked_mul(1_000_000) {
+                Some(value) => value,
+                None => break,
+            };
+            let commission: u128 = amount_full / 100; // 1% commission
+            let amount: u128 = amount_full - commission;
+
+            AccumulatedCommission::<Test>::set(commission);
+            BridgedImbalance::<Test>::set(BridgeAdjustment {
+                bridged_in: amount,
+                bridged_out: 0,
+            });
+
+            assert_eq!(
+                BridgedInflationCurve::<RewardCurve, Test>::era_payout(
+                    total_staked_ideal,
+                    total_issuance + amount,
+                    0
+                ),
+                (commission, 0)
+            );
+        }
+    });
+}