From c3e93f40fe367a4f8f8b6b9b7bae25ebe019d32a Mon Sep 17 00:00:00 2001
From: Alex Ni <12097569+nialexsan@users.noreply.github.com>
Date: Wed, 20 Aug 2025 13:33:55 -0400
Subject: [PATCH 1/2] prevent overflow

---
 cadence/contracts/TidalProtocol.cdc | 60 ++++++++++++++++++++++++-----
 1 file changed, 51 insertions(+), 9 deletions(-)

diff --git a/cadence/contracts/TidalProtocol.cdc b/cadence/contracts/TidalProtocol.cdc
index b1c3e5d0..a68f09e2 100644
--- a/cadence/contracts/TidalProtocol.cdc
+++ b/cadence/contracts/TidalProtocol.cdc
@@ -306,18 +306,60 @@ access(all) contract TidalProtocol {
 
         // Enhanced updateInterestIndices with deposit capacity update
         access(all) fun updateInterestIndices() {
-            let currentTime = getCurrentBlock().timestamp
-            let timeDelta: UFix64 = currentTime - self.lastUpdate
-            self.creditInterestIndex = TidalProtocol.compoundInterestIndex(oldIndex: self.creditInterestIndex, perSecondRate: self.currentCreditRate, elapsedSeconds: timeDelta)
-            self.debitInterestIndex = TidalProtocol.compoundInterestIndex(oldIndex: self.debitInterestIndex, perSecondRate: self.currentDebitRate, elapsedSeconds: timeDelta)
+            let currentTime: UFix64 = getCurrentBlock().timestamp
+            let dt: UFix64 = currentTime - self.lastUpdate
+
+            // No time elapsed or already at cap → nothing to do
+            if dt <= 0.0 {
+                return
+            }
+
+            // Update interest indices (dt > 0 ensures sensible compounding)
+            self.creditInterestIndex = TidalProtocol.compoundInterestIndex(
+                oldIndex: self.creditInterestIndex,
+                perSecondRate: self.currentCreditRate,
+                elapsedSeconds: dt
+            )
+            self.debitInterestIndex = TidalProtocol.compoundInterestIndex(
+                oldIndex: self.debitInterestIndex,
+                perSecondRate: self.currentDebitRate,
+                elapsedSeconds: dt
+            )
+
+            // Record the moment we accounted for
             self.lastUpdate = currentTime
 
-            // Update deposit capacity based on time
-            let newDepositCapacity = self.depositCapacity + (self.depositRate * timeDelta)
-            if newDepositCapacity >= self.depositCapacityCap {
+            // ---- Deposit capacity with overflow-proof, saturating growth ----
+            // Early exits keep gas down and avoid unnecessary math
+            if self.depositCapacity >= self.depositCapacityCap {
+                self.depositCapacity = self.depositCapacityCap
+                return
+            }
+            if self.depositRate <= 0.0 {
+                return
+            }
+
+            // Remaining headroom before hitting the cap
+            let remaining: UFix64 = self.depositCapacityCap - self.depositCapacity
+            if remaining <= 0.0 {
+                self.depositCapacity = self.depositCapacityCap
+                return
+            }
+
+            // Bound the multiplier BEFORE multiplying to prevent overflow:
+            // choose the largest rate that still ensures rate*dt <= remaining
+            let maxRateForStep: UFix64 = remaining / dt
+            let effectiveRate: UFix64 = self.depositRate < maxRateForStep
+                ? self.depositRate
+                : maxRateForStep
+
+            // Safe: growth <= remaining, so the addition cannot overflow
+            let growth: UFix64 = effectiveRate * dt
+            self.depositCapacity = self.depositCapacity + growth
+
+            // Defensive clamp (handles any rounding edge cases)
+            if self.depositCapacity > self.depositCapacityCap {
                 self.depositCapacity = self.depositCapacityCap
-            } else {
-                self.depositCapacity = newDepositCapacity
             }
         }
 

From aedaa869d4c1a2a5da6f77a2d189ef747b5117f2 Mon Sep 17 00:00:00 2001
From: Alex Ni <12097569+nialexsan@users.noreply.github.com>
Date: Tue, 9 Sep 2025 11:10:30 -0400
Subject: [PATCH 2/2] address comments

---
 cadence/contracts/TidalProtocol.cdc | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/cadence/contracts/TidalProtocol.cdc b/cadence/contracts/TidalProtocol.cdc
index a68f09e2..81da3401 100644
--- a/cadence/contracts/TidalProtocol.cdc
+++ b/cadence/contracts/TidalProtocol.cdc
@@ -341,10 +341,6 @@ access(all) contract TidalProtocol {
 
             // Remaining headroom before hitting the cap
             let remaining: UFix64 = self.depositCapacityCap - self.depositCapacity
-            if remaining <= 0.0 {
-                self.depositCapacity = self.depositCapacityCap
-                return
-            }
 
             // Bound the multiplier BEFORE multiplying to prevent overflow:
             // choose the largest rate that still ensures rate*dt <= remaining
@@ -355,10 +351,11 @@ access(all) contract TidalProtocol {
 
             // Safe: growth <= remaining, so the addition cannot overflow
             let growth: UFix64 = effectiveRate * dt
-            self.depositCapacity = self.depositCapacity + growth
 
             // Defensive clamp (handles any rounding edge cases)
-            if self.depositCapacity > self.depositCapacityCap {
+            if self.depositCapacity < (self.depositCapacityCap - growth) {
+                self.depositCapacity = self.depositCapacity + growth
+            } else {
                 self.depositCapacity = self.depositCapacityCap
             }
         }
@@ -970,7 +967,6 @@ access(all) contract TidalProtocol {
             let uintDepositCollateralFactor = DeFiActionsMathUtils.toUInt128(self.collateralFactor[depositType]!)
             var requiredEffectiveCollateral = DeFiActionsMathUtils.mul(uintHealthChange, effectiveDebtAfterWithdrawal)
             requiredEffectiveCollateral = DeFiActionsMathUtils.div(requiredEffectiveCollateral, uintDepositCollateralFactor)
-            requiredEffectiveCollateral = DeFiActionsMathUtils.div(requiredEffectiveCollateral, uintWithdrawBorrowFactor)
 
             // The amount of the token to deposit, in units of the token.
             let collateralTokenCount = DeFiActionsMathUtils.div(requiredEffectiveCollateral, uintDepositPrice)