From 2fc371f93e0e7f2b66dd21256e822da4024a69b1 Mon Sep 17 00:00:00 2001
From: padraic <patrick.morris.310@gmail.com>
Date: Tue, 7 Feb 2023 18:47:20 +0000
Subject: [PATCH 1/2] Invert tstretch when using YieldSpaceMath

---
 contracts/libraries/HyperdriveMath.sol | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/contracts/libraries/HyperdriveMath.sol b/contracts/libraries/HyperdriveMath.sol
index a7a506b58..941b65191 100644
--- a/contracts/libraries/HyperdriveMath.sol
+++ b/contracts/libraries/HyperdriveMath.sol
@@ -129,6 +129,9 @@ library HyperdriveMath {
         if (_isBondOut && _timeRemaining < 1) {
             revert Errors.HyperdriveMath_BaseWithNonzeroTime();
         }
+
+        uint256 oneDivT = FixedPointMath.ONE_18.divDown(_timeStretch);
+
         if (_isBondOut) {
             // If bonds are being purchased, then the entire trade occurs on the
             // curved portion since t = 1.
@@ -138,7 +141,7 @@ library HyperdriveMath {
                 _bondReserveAdjustment,
                 _amountIn,
                 FixedPointMath.ONE_18,
-                _timeStretch,
+                oneDivT,
                 _sharePrice,
                 _initialSharePrice,
                 _isBondOut
@@ -164,7 +167,7 @@ library HyperdriveMath {
                 _bondReserveAdjustment,
                 curveIn,
                 FixedPointMath.ONE_18,
-                _timeStretch,
+                oneDivT,
                 _sharePrice,
                 _initialSharePrice,
                 _isBondOut
@@ -221,6 +224,7 @@ library HyperdriveMath {
             .mulDown(FixedPointMath.ONE_18.sub(_timeRemaining))
             .divDown(_sharePrice);
         uint256 curveOut = _amountOut.mulDown(_timeRemaining);
+        uint256 oneDivT = FixedPointMath.ONE_18.divDown(_timeStretch);
         uint256 curveIn = YieldSpaceMath.calculateInGivenOut(
             // Credit the share reserves by the flat trade.
             _shareReserves.add(flat.divDown(_sharePrice)),
@@ -229,7 +233,7 @@ library HyperdriveMath {
             _bondReserveAdjustment,
             curveOut,
             FixedPointMath.ONE_18,
-            _timeStretch,
+            oneDivT,
             _sharePrice,
             _initialSharePrice,
             false

From d2a1a90356554a5c626b4a8abd5c3c6d0787ca17 Mon Sep 17 00:00:00 2001
From: padraic <patrick.morris.310@gmail.com>
Date: Tue, 7 Feb 2023 18:52:00 +0000
Subject: [PATCH 2/2] comment

---
 contracts/libraries/HyperdriveMath.sol | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/contracts/libraries/HyperdriveMath.sol b/contracts/libraries/HyperdriveMath.sol
index 941b65191..fa5eb08c2 100644
--- a/contracts/libraries/HyperdriveMath.sol
+++ b/contracts/libraries/HyperdriveMath.sol
@@ -130,6 +130,7 @@ library HyperdriveMath {
             revert Errors.HyperdriveMath_BaseWithNonzeroTime();
         }
 
+        // 1/timestretch necessary for YieldSpaceMath
         uint256 oneDivT = FixedPointMath.ONE_18.divDown(_timeStretch);
 
         if (_isBondOut) {
@@ -224,6 +225,7 @@ library HyperdriveMath {
             .mulDown(FixedPointMath.ONE_18.sub(_timeRemaining))
             .divDown(_sharePrice);
         uint256 curveOut = _amountOut.mulDown(_timeRemaining);
+        // 1/timestretch necessary for YieldSpaceMath
         uint256 oneDivT = FixedPointMath.ONE_18.divDown(_timeStretch);
         uint256 curveIn = YieldSpaceMath.calculateInGivenOut(
             // Credit the share reserves by the flat trade.