refactor: use solmate for rounding, test wei instead of gwei

.forge-snapshots/Base-V3DutchOrder-BaseExecuteSingleWithFee.snap

@@ -1 +1 @@
-198780
+198680

.forge-snapshots/Base-V3DutchOrder-ExecuteBatch.snap

@@ -1 +1 @@
-231116
+230916

.forge-snapshots/Base-V3DutchOrder-ExecuteBatchMultipleOutputs.snap

@@ -1 +1 @@
-244626
+244376

.forge-snapshots/Base-V3DutchOrder-ExecuteBatchMultipleOutputsDifferentTokens.snap

@@ -1 +1 @@
-302041
+301741

.forge-snapshots/Base-V3DutchOrder-ExecuteBatchNativeOutput.snap

@@ -1 +1 @@
-224642
+224442

.forge-snapshots/Base-V3DutchOrder-ExecuteSingle.snap

@@ -1 +1 @@
-165165
+165065

.forge-snapshots/Base-V3DutchOrder-ExecuteSingleNativeOutput.snap

@@ -1 +1 @@
-150727
+150627

.forge-snapshots/Base-V3DutchOrder-ExecuteSingleValidation.snap

@@ -1 +1 @@
-174481
+174381

.forge-snapshots/Base-V3DutchOrder-RevertInvalidNonce.snap

@@ -1 +1 @@
-43785
+43685

.forge-snapshots/Base-V3DutchOrder-V3-ExclusiveFiller.snap

@@ -1 +1 @@
-169089
+168989

.forge-snapshots/Base-V3DutchOrder-V3-InputOverride.snap

@@ -1 +1 @@
-169170
+169070

.forge-snapshots/Base-V3DutchOrder-V3-OutputOverride.snap

@@ -1 +1 @@
-169113
+169013

src/reactors/V3DutchOrderReactor.sol

@@ -12,6 +12,7 @@ import {FixedPointMathLib} from "solmate/src/utils/FixedPointMathLib.sol";
 import {MathExt} from "../lib/MathExt.sol";
 import {Math} from "openzeppelin-contracts/utils/math/Math.sol";
 import {CosignerLib} from "../lib/CosignerLib.sol";
+import {SafeCast} from "openzeppelin-contracts/utils/math/SafeCast.sol";
 
 /// @notice Reactor for V3 dutch orders
 /// @dev V3 orders must be cosigned by the specified cosigner to override starting block and value
@@ -109,26 +110,32 @@ contract V3DutchOrderReactor is BaseReactor {
     }
 
     function _updateWithGasAdjustment(V3DutchOrder memory order) internal view {
-        // positive means an increase in gas
-        int256 gasDeltaGwei = block.basefee.sub(order.startingBaseFee);
+        // Positive means an increase in gas
+        int256 gasDeltaWei = block.basefee.sub(order.startingBaseFee);
 
-        // Gas increase should increase input (round up when positive, down when negative)
-        int256 inputDelta = gasDeltaGwei >= 0
-            ? (int256(order.baseInput.adjustmentPerGweiBaseFee) * gasDeltaGwei + 1 gwei - 1) / 1 gwei
-            : (int256(order.baseInput.adjustmentPerGweiBaseFee) * gasDeltaGwei) / 1 gwei;
+        // Round in favor of swapper
+        int256 inputDelta = _computeDelta(order.baseInput.adjustmentPerGweiBaseFee, gasDeltaWei);
         order.baseInput.startAmount = order.baseInput.startAmount.boundedAdd(inputDelta, 0, order.baseInput.maxAmount);
 
-        // Gas increase should decrease output (round down when positive, up when negative)
         uint256 outputsLength = order.baseOutputs.length;
         for (uint256 i = 0; i < outputsLength; i++) {
             V3DutchOutput memory output = order.baseOutputs[i];
-            int256 outputDelta = gasDeltaGwei >= 0
-                ? (int256(output.adjustmentPerGweiBaseFee) * gasDeltaGwei) / 1 gwei
-                : (int256(output.adjustmentPerGweiBaseFee) * gasDeltaGwei - 1 gwei + 1) / 1 gwei;
+            // Round in favor of swapper
+            int256 outputDelta = _computeDelta(output.adjustmentPerGweiBaseFee, gasDeltaWei);
             output.startAmount = output.startAmount.boundedSub(outputDelta, output.minAmount, type(uint256).max);
         }
     }
 
+    function _computeDelta(uint256 adjustmentPerGweiBaseFee, int256 gasDeltaWei) internal pure returns (int256) {
+        if (gasDeltaWei >= 0) {
+            // Gas increase: round adjustment down to decrease amount added to input or subtracted from output
+            return int256(adjustmentPerGweiBaseFee.mulDivDown(uint256(gasDeltaWei), 1 gwei));
+        } else {
+            // Gas decrease: round adjustment up to increase amount added to output or subtracted from input
+            return -int256(adjustmentPerGweiBaseFee.mulDivUp(SafeCast.toUint256(-gasDeltaWei), 1 gwei));
+        }
+    }
+
     /// @notice validate the dutch order fields
     /// - deadline must have not passed
     /// - cosigner is valid if specified

test/reactors/V3DutchOrderReactor.t.sol

@@ -1406,47 +1406,49 @@ contract V3DutchOrderTest is PermitSignature, DeployPermit2, BaseReactorTest {
         vm.roll(currentBlock);
         vm.fee(1 gwei);
 
-        // Order with 0.8 gwei gas adjustments
+        // Order with 1 wei gas adjustments
         SignedOrder memory order = generateOrder(
             TestDutchOrderSpec({
                 currentBlock: currentBlock,
                 startBlock: currentBlock,
                 deadline: currentBlock + 21,
-                input: V3DutchInput(tokenIn, 100 ether, CurveBuilder.emptyCurve(), 101 ether, 0.8 gwei),
+                input: V3DutchInput(tokenIn, 1000, CurveBuilder.emptyCurve(), 1100, 1),
                 outputs: OutputsBuilder.singleV3Dutch(
-                    V3DutchOutput(address(tokenOut), 100 ether, CurveBuilder.emptyCurve(), address(0), 99 ether, 0.8 gwei)
+                    V3DutchOutput(address(tokenOut), 1000, CurveBuilder.emptyCurve(), address(0), 900, 1)
                 )
             })
         );
 
         // Test gas increase
-        vm.fee(2 gwei);
+        vm.fee(1.5 gwei);
         ResolvedOrder memory resolvedOrder = quoter.quote(order.order, order.sig);
-        assertEq(resolvedOrder.input.amount, 100 ether + 0.8 gwei, "Input should round up for positive gas change");
-        assertEq(resolvedOrder.outputs[0].amount, 100 ether - 0.8 gwei, "Output should round down for positive gas change");
+        // The gas adjusted input would be 1000.5, which should round down to 1000
+        assertEq(resolvedOrder.input.amount, 1000, "Input should round down");
+        // The gas adjusted output would be 999.5, which should round up to 1000
+        assertEq(resolvedOrder.outputs[0].amount, 1000, "Output should round up");
 
         // Test gas decrease
         vm.fee(0.5 gwei);
         resolvedOrder = quoter.quote(order.order, order.sig);
-        assertEq(resolvedOrder.input.amount, 100 ether - 0.4 gwei, "Input should round down for negative gas change");
-        assertEq(resolvedOrder.outputs[0].amount, 100 ether + 0.4 gwei, "Output should round up for negative gas change");
-
-        // Test gas half
-        vm.fee(0.5 gwei);
-        resolvedOrder = quoter.quote(order.order, order.sig);
-        assertEq(resolvedOrder.input.amount, 100 ether - 0.4 gwei, "Input should round down for gas halving change");
-        assertEq(resolvedOrder.outputs[0].amount, 100 ether + 0.4 gwei, "Output should round up for exact gas halving change");
+        // The gas adjusted input would be 999.5, which should round down to 999
+        assertEq(resolvedOrder.input.amount, 999, "Input should round down");
+        // The gas adjusted output would be 1000.5, which should round up to 1001
+        assertEq(resolvedOrder.outputs[0].amount, 1001, "Output should round up");
 
         // Test smaller gas changes
         vm.fee(1.1 gwei);
         resolvedOrder = quoter.quote(order.order, order.sig);
-        assertEq(resolvedOrder.input.amount, 100 ether + 0.08 gwei, "Input should handle small positive gas changes");
-        assertEq(resolvedOrder.outputs[0].amount, 100 ether - 0.08 gwei, "Output should handle small positive gas changes");
+        // The gas adjusted input would be 1000.1, which should round down to 1000
+        assertEq(resolvedOrder.input.amount, 1000, "Input should round down");
+        // The gas adjusted output would be 999.9, which should round up to 1000
+        assertEq(resolvedOrder.outputs[0].amount, 1000, "Output should round up");
 
         vm.fee(0.9 gwei);
         resolvedOrder = quoter.quote(order.order, order.sig);
-        assertEq(resolvedOrder.input.amount, 100 ether - 0.08 gwei, "Input should handle small negative gas changes");
-        assertEq(resolvedOrder.outputs[0].amount, 100 ether + 0.08 gwei, "Output should handle small negative gas changes");
+        // The gas adjusted input would be 999.9, which should round down to 999
+        assertEq(resolvedOrder.input.amount, 999, "Input should round down");
+        // The gas adjusted output would be 1000.1, which should round up to 1001
+        assertEq(resolvedOrder.outputs[0].amount, 1001, "Output should round up");
     }
 
     /* Test helpers */