gas optimization: leave one wei feature

contracts/GenericSwap.sol

@@ -67,16 +67,19 @@ contract GenericSwap is IGenericSwap, TokenCollector, EIP712 {
 
         if (_inputToken.isETH()) {
             if (msg.value != _swapData.takerTokenAmount) revert InvalidMsgValue();
-        }
-
-        if (!_inputToken.isETH()) {
+        } else {
             if (msg.value != 0) revert InvalidMsgValue();
             _collect(_inputToken, _authorizedUser, _swapData.maker, _swapData.takerTokenAmount, _takerTokenPermit);
         }
 
         IStrategy(_swapData.maker).executeStrategy{ value: msg.value }(_inputToken, _outputToken, _swapData.takerTokenAmount, _swapData.strategyData);
 
         returnAmount = _outputToken.getBalance(address(this));
+        if (returnAmount > 1) {
+            unchecked {
+                --returnAmount;
+            }
+        }
         if (returnAmount < _swapData.minMakerTokenAmount) revert InsufficientOutput();
 
         _outputToken.transferTo(_swapData.recipient, returnAmount);

contracts/SmartOrderStrategy.sol

@@ -57,6 +57,11 @@ contract SmartOrderStrategy is ISmartOrderStrategy, AdminManagement {
             }
         }
         uint256 selfBalance = Asset.getBalance(outputToken, address(this));
+        if (selfBalance > 1) {
+            unchecked {
+                --selfBalance;
+            }
+        }
         Asset.transferTo(outputToken, payable(genericSwap), selfBalance);
     }
 
@@ -65,7 +70,13 @@ contract SmartOrderStrategy is ISmartOrderStrategy, AdminManagement {
 
         // replace amount if ratio != 0
         if (_inputRatio != 0) {
+            // leave one wei
             uint256 inputTokenBalance = IERC20(_inputToken).balanceOf(address(this));
+            if (inputTokenBalance > 1) {
+                unchecked {
+                    --inputTokenBalance;
+                }
+            }
 
             // calculate input amount if ratio should be applied
             if (_inputRatio != Constant.BPS_MAX) {

test/forkMainnet/GenericSwap.t.sol

@@ -62,6 +62,12 @@ contract GenericSwapTest is Test, Tokens, BalanceUtil, Permit2Helper, SigHelper
 
         genericSwap = new GenericSwap(UNISWAP_PERMIT2_ADDRESS, address(allowanceTarget));
         smartStrategy = new SmartOrderStrategy(strategyAdmin, address(genericSwap), WETH_ADDRESS);
+
+        // deposit 1 wei in SOR and GS
+        deal(DAI_ADDRESS, address(smartStrategy), 1 wei);
+        deal(DAI_ADDRESS, address(genericSwap), 1 wei);
+        deal(address(genericSwap), 1 wei);
+
         mockStrategy = new MockStrategy();
         vm.prank(strategyAdmin);
         address[] memory tokenList = new address[](1);

test/forkMainnet/SmartOrderStrategy/IntegrationV6.t.sol

@@ -46,6 +46,9 @@ contract IntegrationV6Test is SmartOrderStrategyTest, SigHelper {
         vm.prank(strategyOwner);
         smartOrderStrategy.approveTokens(tokenList, spenders);
 
+        deal(LON_ADDRESS, address(smartOrderStrategy), 1 wei);
+        deal(DAI_ADDRESS, address(smartOrderStrategy), 1 wei);
+
         // maker approves RFQ & LO
         setTokenBalanceAndApprove(maker, address(rfq), tokens, 100000);
         setTokenBalanceAndApprove(maker, address(limitOrderSwap), tokens, 100000);

test/forkMainnet/SmartOrderStrategy/Setup.t.sol

@@ -40,6 +40,11 @@ contract SmartOrderStrategyTest is Test, Tokens, BalanceUtil {
             setERC20Balance(tokenList[i], genericSwap, 10000);
         }
 
+        deal(USDC_ADDRESS, address(smartOrderStrategy), 1 wei);
+        deal(USDT_ADDRESS, address(smartOrderStrategy), 1 wei);
+        deal(WETH_ADDRESS, address(smartOrderStrategy), 1 wei);
+        deal(WBTC_ADDRESS, address(smartOrderStrategy), 1 wei);
+
         SmartOrderStrategy.Operation[] memory operations = new SmartOrderStrategy.Operation[](1);
         defaultOpsData = abi.encode(operations);