From e56765f067af61839fbcd3423ba7b1a5df6ddca9 Mon Sep 17 00:00:00 2001
From: Matthew Pereira <matthewdavidpereira@gmail.com>
Date: Sun, 22 Dec 2024 11:32:24 -0800
Subject: [PATCH] Fix math for exact out swaps for CPP

---
 packages/foundry/contracts/pools/ConstantProductPool.sol | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/foundry/contracts/pools/ConstantProductPool.sol b/packages/foundry/contracts/pools/ConstantProductPool.sol
index 898e7ed2..623dfc16 100644
--- a/packages/foundry/contracts/pools/ConstantProductPool.sol
+++ b/packages/foundry/contracts/pools/ConstantProductPool.sol
@@ -40,8 +40,8 @@ contract ConstantProductPool is BalancerPoolToken, IBasePool {
             amountCalculatedScaled18 = (poolBalancetokenOut * amountTokenIn) / (poolBalancetokenIn + amountTokenIn);
         } else {
             uint256 amountTokenOut = params.amountGivenScaled18; // dy
-            // dx = (X * dy) / (Y + dx)
-            amountCalculatedScaled18 = (poolBalancetokenIn * amountTokenOut) / (poolBalancetokenOut + amountTokenOut);
+            // dx = (X * dy) / (Y - dy)
+            amountCalculatedScaled18 = (poolBalancetokenIn * amountTokenOut) / (poolBalancetokenOut - amountTokenOut);
         }
     }