implement muldiv without overflow and underflow

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

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)
+            );
+        }
+    });
+}