Avoid recomputing amountIn when exactIn and `amountRemainingLessF… (#718)

shuhuiluo · web-flow · commit 8f147f1ed3b2 · 2024-08-29T17:00:36.000-04:00
Avoid recomputing `amountIn` when `exactIn` and `amountRemainingLessFee &lt; amountIn`

Simplify the flow in SwapMath library by removing unnecessary calculations related to input amounts. The removed calculations are replaced with a direct assignment of the remaining amount which simplifies the logic. Moreover, the potential for any rounding issues is significantly reduced.
diff --git a/.forge-snapshots/SwapMath_oneForZero_exactInCapped.snap b/.forge-snapshots/SwapMath_oneForZero_exactInCapped.snap
@@ -1 +1 @@
-1220
+1192
diff --git a/.forge-snapshots/SwapMath_oneForZero_exactInPartial.snap b/.forge-snapshots/SwapMath_oneForZero_exactInPartial.snap
@@ -1 +1 @@
-1544
+1261
diff --git a/.forge-snapshots/SwapMath_zeroForOne_exactInCapped.snap b/.forge-snapshots/SwapMath_zeroForOne_exactInCapped.snap
@@ -1 +1 @@
-1133
+1130
diff --git a/.forge-snapshots/SwapMath_zeroForOne_exactInPartial.snap b/.forge-snapshots/SwapMath_zeroForOne_exactInPartial.snap
@@ -1 +1 @@
-1859
+1443
diff --git a/.forge-snapshots/poolManager bytecode size.snap b/.forge-snapshots/poolManager bytecode size.snap
@@ -1 +1 @@
-23947
+23924
diff --git a/.forge-snapshots/simple swap with native.snap b/.forge-snapshots/simple swap with native.snap
@@ -1 +1 @@
-108786
+108354
diff --git a/.forge-snapshots/simple swap.snap b/.forge-snapshots/simple swap.snap
@@ -1 +1 @@
-123629
+123197
diff --git a/.forge-snapshots/swap CA custom curve + swap noop.snap b/.forge-snapshots/swap CA custom curve + swap noop.snap
@@ -1 +1 @@
-126846
+126854
diff --git a/.forge-snapshots/swap CA fee on unspecified.snap b/.forge-snapshots/swap CA fee on unspecified.snap
@@ -1 +1 @@
-155069
+154637
diff --git a/.forge-snapshots/swap against liquidity with native token.snap b/.forge-snapshots/swap against liquidity with native token.snap
@@ -1 +1 @@
-105938
+105477
diff --git a/.forge-snapshots/swap against liquidity.snap b/.forge-snapshots/swap against liquidity.snap
@@ -1 +1 @@
-117029
+116568
diff --git a/.forge-snapshots/swap burn 6909 for input.snap b/.forge-snapshots/swap burn 6909 for input.snap
@@ -1 +1 @@
-129087
+129103
diff --git a/.forge-snapshots/swap burn native 6909 for input.snap b/.forge-snapshots/swap burn native 6909 for input.snap
@@ -1 +1 @@
-118542
+118553
diff --git a/.forge-snapshots/swap mint native output as 6909.snap b/.forge-snapshots/swap mint native output as 6909.snap
@@ -1 +1 @@
-139929
+139616
diff --git a/.forge-snapshots/swap mint output as 6909.snap b/.forge-snapshots/swap mint output as 6909.snap
@@ -1 +1 @@
-155469
+155037
diff --git a/.forge-snapshots/swap skips hook call if hook is caller.snap b/.forge-snapshots/swap skips hook call if hook is caller.snap
@@ -1 +1 @@
-207062
+206169
diff --git a/.forge-snapshots/swap with dynamic fee.snap b/.forge-snapshots/swap with dynamic fee.snap
@@ -1 +1 @@
-139661
+139229
diff --git a/.forge-snapshots/swap with hooks.snap b/.forge-snapshots/swap with hooks.snap
@@ -1 +1 @@
-132666
+132205
diff --git a/.forge-snapshots/swap with lp fee and protocol fee.snap b/.forge-snapshots/swap with lp fee and protocol fee.snap
@@ -1 +1 @@
-169405
+169416
diff --git a/.forge-snapshots/swap with return dynamic fee.snap b/.forge-snapshots/swap with return dynamic fee.snap
@@ -1 +1 @@
-145987
+145555
diff --git a/.forge-snapshots/update dynamic fee in before swap.snap b/.forge-snapshots/update dynamic fee in before swap.snap
@@ -1 +1 @@
-148264
+147832
diff --git a/src/libraries/SwapMath.sol b/src/libraries/SwapMath.sol
@@ -73,12 +73,11 @@ library SwapMath {
                         ? amountIn
                         : FullMath.mulDivRoundingUp(amountIn, _feePips, MAX_SWAP_FEE - _feePips);
                 } else {
+                    // exhaust the remaining amount
+                    amountIn = amountRemainingLessFee;
                     sqrtPriceNextX96 = SqrtPriceMath.getNextSqrtPriceFromInput(
                         sqrtPriceCurrentX96, liquidity, amountRemainingLessFee, zeroForOne
                     );
-                    amountIn = zeroForOne
-                        ? SqrtPriceMath.getAmount0Delta(sqrtPriceNextX96, sqrtPriceCurrentX96, liquidity, true)
-                        : SqrtPriceMath.getAmount1Delta(sqrtPriceCurrentX96, sqrtPriceNextX96, liquidity, true);
                     // we didn't reach the target, so take the remainder of the maximum input as fee
                     feeAmount = uint256(-amountRemaining) - amountIn;
                 }
diff --git a/test/libraries/SwapMath.t.sol b/test/libraries/SwapMath.t.sol
@@ -140,12 +140,12 @@ contract SwapMathTest is Test, GasSnapshot {
         assertEq(sqrtQ, 1);
     }
 
-    function test_computeSwapStep_entireInputAmountTakenAsFee() public pure {
+    function test_computeSwapStep_notEntireInputAmountTakenAsFee() public pure {
         (uint160 sqrtQ, uint256 amountIn, uint256 amountOut, uint256 feeAmount) =
             SwapMath.computeSwapStep(2413, 79887613182836312, 1985041575832132834610021537970, -10, 1872);
 
-        assertEq(amountIn, 0);
-        assertEq(feeAmount, 10);
+        assertEq(amountIn, 9);
+        assertEq(feeAmount, 1);
         assertEq(amountOut, 0);
         assertEq(sqrtQ, 2413);
     }
