improve and simplify fee split calculation, change feeMultiplier to just fee

Author: hoytech

src/EulerSwap.sol

@@ -16,19 +16,16 @@ contract EulerSwap is IEulerSwap, EVCUtil {
 
     bytes32 public constant curve = bytes32("EulerSwap v1");
 
-    uint256 public constant protocolFee = 0.1e18;
-    address public constant protocolFeeRecipient = address(0);
-
     address public immutable vault0;
     address public immutable vault1;
     address public immutable asset0;
     address public immutable asset1;
     address public immutable eulerAccount;
     uint112 public immutable equilibriumReserve0;
     uint112 public immutable equilibriumReserve1;
-    uint256 public immutable feeMultiplier;
-    uint256 private immutable feeMultiplierProtocol;
-    uint256 private immutable feeMultiplierLP;
+    uint256 public immutable fee;
+    uint256 public immutable protocolFee;
+    address public immutable protocolFeeRecipient;
 
     uint256 public immutable priceX;
     uint256 public immutable priceY;
@@ -88,9 +85,9 @@ contract EulerSwap is IEulerSwap, EVCUtil {
         equilibriumReserve1 = params.equilibriumReserve1;
         reserve0 = params.currReserve0;
         reserve1 = params.currReserve1;
-        feeMultiplier = 1e18 - params.fee;
-        feeMultiplierProtocol = 1e18 - (params.fee * protocolFee / 1e18);
-        feeMultiplierLP = feeMultiplier * 1e18 / feeMultiplierProtocol;
+        fee = params.fee;
+        protocolFee = 0.1e18;
+        protocolFeeRecipient = address(0);
 
         // Curve params
 
@@ -226,10 +223,16 @@ contract EulerSwap is IEulerSwap, EVCUtil {
         uint256 amount = IERC20(asset).balanceOf(address(this));
         if (amount == 0) return 0;
 
+        uint256 feeAmount = amount * fee / 1e18;
+
         {
-            uint256 feeAmount = amount - (amount * feeMultiplierProtocol / 1e18);
-            IERC20(asset).transfer(protocolFeeRecipient, feeAmount);
-            amount -= feeAmount;
+            uint256 protocolFeeAmount = feeAmount * protocolFee / 1e18;
+
+            if (protocolFeeAmount != 0) {
+                IERC20(asset).transfer(protocolFeeRecipient, protocolFeeAmount);
+                amount -= protocolFeeAmount;
+                feeAmount -= protocolFeeAmount;
+            }
         }
 
         uint256 deposited;
@@ -257,7 +260,7 @@ contract EulerSwap is IEulerSwap, EVCUtil {
             deposited += amount;
         }
 
-        return (deposited * feeMultiplierLP + (1e18 - 1)) / 1e18;
+        return deposited > feeAmount ? deposited - feeAmount : 0;
     }
 
     /// @notice Approves tokens for a given vault, supporting both standard approvals and permit2

src/EulerSwapFactory.sol

@@ -23,7 +23,7 @@ contract EulerSwapFactory is IEulerSwapFactory, EVCUtil {
         address indexed asset1,
         address vault0,
         address vault1,
-        uint256 indexed feeMultiplier,
+        uint256 indexed fee,
         address eulerAccount,
         uint256 reserve0,
         uint256 reserve1,
@@ -70,7 +70,7 @@ contract EulerSwapFactory is IEulerSwapFactory, EVCUtil {
             pool.asset1(),
             params.vault0,
             params.vault1,
-            pool.feeMultiplier(),
+            pool.fee(),
             params.eulerAccount,
             params.currReserve0,
             params.currReserve1,

src/EulerSwapPeriphery.sol

@@ -105,11 +105,11 @@ contract EulerSwapPeriphery is IEulerSwapPeriphery {
         );
         require(amount <= type(uint112).max, SwapLimitExceeded());
 
-        uint256 feeMultiplier = eulerSwap.feeMultiplier();
+        uint256 fee = eulerSwap.fee();
         (uint112 reserve0, uint112 reserve1,) = eulerSwap.getReserves();
 
-        // exactIn: decrease received amountIn, rounding down
-        if (exactIn) amount = amount * feeMultiplier / 1e18;
+        // exactIn: decrease effective amountIn
+        if (exactIn) amount = amount - (amount * fee / 1e18);
 
         bool asset0IsInput = checkTokens(eulerSwap, tokenIn, tokenOut);
         (uint256 inLimit, uint256 outLimit) = calcLimits(eulerSwap, asset0IsInput);
@@ -124,8 +124,8 @@ contract EulerSwapPeriphery is IEulerSwapPeriphery {
             require(amount <= outLimit && quote <= inLimit, SwapLimitExceeded());
         }
 
-        // exactOut: increase required quote(amountIn), rounding up
-        if (!exactIn) quote = (quote * 1e18 + (feeMultiplier - 1)) / feeMultiplier;
+        // exactOut: inflate required amountIn
+        if (!exactIn) quote = (quote * 1e18) / (1e18 - fee);
 
         return quote;
     }

src/interfaces/IEulerSwap.sol

@@ -50,7 +50,9 @@ interface IEulerSwap {
     function eulerAccount() external view returns (address);
     function equilibriumReserve0() external view returns (uint112);
     function equilibriumReserve1() external view returns (uint112);
-    function feeMultiplier() external view returns (uint256);
+    function fee() external view returns (uint256);
+    function protocolFee() external view returns (uint256);
+    function protocolFeeRecipient() external view returns (address);
     /// @notice Returns the current reserves of the pool
     /// @return reserve0 The amount of asset0 in the pool
     /// @return reserve1 The amount of asset1 in the pool