feat, test: handle long-term orders to properly decay (#304)

* feat, test: handle long-term orders to properly decay

* refactor: fuzz inputs match decay function params

* style: forge fmt

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

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-199162
+199140

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

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+231899

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

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+245748

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

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+303522

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

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+225426

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

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+165523

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

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+151085

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

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+174834

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

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+44158

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

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+169458

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

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+169539

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

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+169482

.forge-snapshots/V3-DutchDecay.snap

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+13371

.forge-snapshots/V3-DutchDecayBounded.snap

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+1206

.forge-snapshots/V3-DutchDecayFullyDecayed.snap

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+6779

.forge-snapshots/V3-DutchDecayFullyDecayedNegative.snap

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+6467

.forge-snapshots/V3-DutchDecayNegative.snap

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+1265

.forge-snapshots/V3-DutchDecayNoDecayYet.snap

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+4697

.forge-snapshots/V3-DutchDecayNoDecayYetNegative.snap

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.forge-snapshots/V3-DutchDecayRange.snap

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+1265

.forge-snapshots/V3-ExtendedMultiPointDutchDecay.snap

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+88450

.forge-snapshots/V3-MultiPointDutchDecay.snap

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+26539

src/lib/NonlinearDutchDecayLib.sol

@@ -5,6 +5,7 @@ import {OutputToken, InputToken} from "../base/ReactorStructs.sol";
 import {V3DutchOutput, V3DutchInput, NonlinearDutchDecay} from "../lib/V3DutchOrderLib.sol";
 import {FixedPointMathLib} from "solmate/src/utils/FixedPointMathLib.sol";
 import {MathExt} from "./MathExt.sol";
+import {Math} from "openzeppelin-contracts/utils/math/Math.sol";
 import {Uint16ArrayLibrary, Uint16Array, fromUnderlying} from "../types/Uint16Array.sol";
 import {DutchDecayLib} from "./DutchDecayLib.sol";
 
@@ -39,8 +40,9 @@ library NonlinearDutchDecayLib {
         if (decayStartBlock >= block.number || curve.relativeAmounts.length == 0) {
             return startAmount.bound(minAmount, maxAmount);
         }
-
-        uint16 blockDelta = uint16(block.number - decayStartBlock);
+        // If the blockDelta is larger than type(uint16).max, a downcast overflow will occur
+        // We prevent this by capping the blockDelta to type(uint16).max to express a full decay
+        uint16 blockDelta = uint16(Math.min(block.number - decayStartBlock, type(uint16).max));
         (uint16 startPoint, uint16 endPoint, int256 relStartAmount, int256 relEndAmount) =
             locateCurvePosition(curve, blockDelta);
         // get decay of only the relative amounts

test/lib/NonLinearDutchDecayLib.t.sol

@@ -8,6 +8,7 @@ import {DutchDecayLib} from "../../src/lib/DutchDecayLib.sol";
 import {NonlinearDutchDecayLib} from "../../src/lib/NonlinearDutchDecayLib.sol";
 import {V3DutchOutput, V3DutchInput, NonlinearDutchDecay} from "../../src/lib/V3DutchOrderLib.sol";
 import {Uint16Array, toUint256} from "../../src/types/Uint16Array.sol";
+import {Math} from "openzeppelin-contracts/utils/math/Math.sol";
 import {ArrayBuilder} from "../util/ArrayBuilder.sol";
 import {CurveBuilder} from "../util/CurveBuilder.sol";
 
@@ -474,4 +475,44 @@ contract NonlinearDutchDecayLibTest is Test, GasSnapshot {
         vm.expectRevert(NonlinearDutchDecayLib.InvalidDecayCurve.selector);
         mockNonlinearDutchDecayLibContract.decay(curve, startAmount, decayStartBlock, 1 ether, 1 ether);
     }
+
+    function testFuzzDutchDecayBeyondUint16Max(
+        uint16 lastValidBlock, // For curve
+        uint256 decayAmountFuzz, // For curve
+        // decay(curve, startAmount, decayStartBlock, minAmount, maxAmount);
+        uint256 startAmount,
+        uint256 decayStartBlock,
+        uint256 minAmount,
+        uint256 maxAmount,
+        uint256 currentBlock
+    ) public {
+        vm.assume(decayStartBlock < type(uint256).max - type(uint16).max);
+        vm.assume(lastValidBlock > 0);
+        vm.assume(startAmount > 0 && startAmount < uint256(type(int256).max));
+        vm.assume(maxAmount >= startAmount);
+        minAmount = bound(minAmount, 0, startAmount);
+        // bound only takes uint256, so we need to limit decayAmountFuzz to int256.max
+        // because we cast it to int256 in the decay function
+        decayAmountFuzz = bound(decayAmountFuzz, minAmount, startAmount);
+
+        // Testing that we get a fully decayed curve instead of overflowed mistake
+        // This will happen when the block delta is larger than type(uint16).max
+        vm.assume(currentBlock > decayStartBlock + type(uint16).max);
+
+        uint16[] memory blocks = new uint16[](1);
+        blocks[0] = lastValidBlock;
+
+        int256[] memory decayAmounts = new int256[](1);
+        decayAmounts[0] = int256(decayAmountFuzz);
+
+        NonlinearDutchDecay memory curve = CurveBuilder.multiPointCurve(blocks, decayAmounts);
+
+        vm.roll(currentBlock);
+        uint256 decayed = NonlinearDutchDecayLib.decay(curve, startAmount, decayStartBlock, minAmount, maxAmount);
+        assertEq(
+            decayed,
+            Math.max(startAmount - decayAmountFuzz, minAmount),
+            "Should be fully decayed for block delta beyond uint16.max"
+        );
+    }
 }