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Optimisation of the balance/debt increase math #707

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Optimisation of the balance/debt increase math #707

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43 changes: 11 additions & 32 deletions contracts/protocol/libraries/logic/ReserveLogic.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -211,15 +211,6 @@ library ReserveLogic {
);
}

struct AccrueToTreasuryLocalVars {
uint256 prevTotalStableDebt;
uint256 prevTotalVariableDebt;
uint256 currTotalVariableDebt;
uint256 cumulatedStableInterest;
uint256 totalDebtAccrued;
uint256 amountToMint;
}

/**
* @notice Mints part of the repaid interest to the reserve treasury as a function of the reserve factor for the
* specific asset.
Expand All @@ -230,47 +221,35 @@ library ReserveLogic {
DataTypes.ReserveData storage reserve,
DataTypes.ReserveCache memory reserveCache
) internal {
AccrueToTreasuryLocalVars memory vars;

if (reserveCache.reserveFactor == 0) {
return;
}

//calculate the total variable debt at moment of the last interaction
vars.prevTotalVariableDebt = reserveCache.currScaledVariableDebt.rayMul(
reserveCache.currVariableBorrowIndex
);

//calculate the new total variable debt after accumulation of the interest on the index
vars.currTotalVariableDebt = reserveCache.currScaledVariableDebt.rayMul(
reserveCache.nextVariableBorrowIndex
// calculate the total variable debt increase after the moment of the last interaction
uint256 variableDebtIncrease = reserveCache.currScaledVariableDebt.rayMul(
reserveCache.nextVariableBorrowIndex - reserveCache.currVariableBorrowIndex
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Same

);

//calculate the stable debt until the last timestamp update
vars.cumulatedStableInterest = MathUtils.calculateCompoundedInterest(
uint256 cumulatedStableInterest = MathUtils.calculateCompoundedInterest(
reserveCache.currAvgStableBorrowRate,
reserveCache.stableDebtLastUpdateTimestamp,
reserveCache.reserveLastUpdateTimestamp
);

vars.prevTotalStableDebt = reserveCache.currPrincipalStableDebt.rayMul(
vars.cumulatedStableInterest
uint256 prevTotalStableDebt = reserveCache.currPrincipalStableDebt.rayMul(
cumulatedStableInterest
);

//debt accrued is the sum of the current debt minus the sum of the debt at the last update
vars.totalDebtAccrued =
vars.currTotalVariableDebt +
uint256 totalDebtAccrued = variableDebtIncrease +
reserveCache.currTotalStableDebt -
vars.prevTotalVariableDebt -
vars.prevTotalStableDebt;
prevTotalStableDebt;

vars.amountToMint = vars.totalDebtAccrued.percentMul(reserveCache.reserveFactor);
uint256 amountToMint = totalDebtAccrued.percentMul(reserveCache.reserveFactor);

if (vars.amountToMint != 0) {
reserve.accruedToTreasury += vars
.amountToMint
.rayDiv(reserveCache.nextLiquidityIndex)
.toUint128();
if (amountToMint != 0) {
reserve.accruedToTreasury += amountToMint.rayDiv(reserveCache.nextLiquidityIndex).toUint128();
}
}

Expand Down
7 changes: 2 additions & 5 deletions contracts/protocol/tokenization/base/ScaledBalanceTokenBase.sol
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Expand Up @@ -76,9 +76,7 @@ abstract contract ScaledBalanceTokenBase is MintableIncentivizedERC20, IScaledBa
require(amountScaled != 0, Errors.INVALID_MINT_AMOUNT);

uint256 scaledBalance = super.balanceOf(onBehalfOf);
uint256 balanceIncrease = scaledBalance.rayMul(index) -
scaledBalance.rayMul(_userState[onBehalfOf].additionalData);

uint256 balanceIncrease = scaledBalance.rayMul(index - _userState[onBehalfOf].additionalData);
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This approach is not exactly equivalent to the other because of math rounding and precision. We should stick to the original approach

_userState[onBehalfOf].additionalData = index.toUint128();

_mint(onBehalfOf, amountScaled.toUint128());
Expand Down Expand Up @@ -109,8 +107,7 @@ abstract contract ScaledBalanceTokenBase is MintableIncentivizedERC20, IScaledBa
require(amountScaled != 0, Errors.INVALID_BURN_AMOUNT);

uint256 scaledBalance = super.balanceOf(user);
uint256 balanceIncrease = scaledBalance.rayMul(index) -
scaledBalance.rayMul(_userState[user].additionalData);
uint256 balanceIncrease = scaledBalance.rayMul(index - _userState[user].additionalData);

_userState[user].additionalData = index.toUint128();

Expand Down