move functions from CurveLib into more appropriate places: new CurveExtras library, and tests

Author: hoytech

docs/architecture.md

@@ -25,6 +25,7 @@ The above contracts depend on libraries:
 * `FundsLib`: Moving tokens: approvals and transfers in/out
 * `CurveLib`: Mathematical routines for calculating the EulerSwap curve
 * `QuoteLib`: Computing quotes. This involves invoking the logic from `CurveLib`, as well as taking into account other limitations such as vault utilisation, supply caps, etc.
+* `CurveExtrasLib`: Extra utilities for curve computations. Not used in the EulerSwap itself, but potentially useful for integrators.
 
 And some utilities:
 

src/libraries/CurveExtrasLib.sol

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.27;
+
+import {Math} from "openzeppelin-contracts/utils/math/Math.sol";
+
+library CurveExtrasLib {
+    /// @dev EulerSwap derivative helper function to find the price after a swap
+    /// Pre-conditions: 0 < x <= x0, 1 <= {px,py} <= 1e36, {x0,y0} <= type(uint112).max, c <= 1e18
+    function df_dx(uint256 x, uint256 px, uint256 py, uint256 x0, uint256 y0, uint256 c)
+        internal
+        pure
+        returns (int256)
+    {
+        uint256 r = Math.mulDiv(x0 * x0 / x, 1e18, x, Math.Rounding.Ceil);
+        return -int256(px * (c + (1e18 - c) * r / 1e18) / py);
+    }
+}

src/libraries/CurveLib.sol

@@ -116,39 +116,4 @@ library CurveLib {
             scale = 1;
         }
     }
-
-    /// @dev Less efficient method to compute fInverse. Useful for testing.
-    function binarySearch(IEulerSwap.Params memory p, uint256 newReserve1, uint256 xMin, uint256 xMax)
-        internal
-        pure
-        returns (uint256)
-    {
-        if (xMin < 1) {
-            xMin = 1;
-        }
-        while (xMin < xMax) {
-            uint256 xMid = (xMin + xMax) / 2;
-            uint256 fxMid = f(xMid, p.priceX, p.priceY, p.equilibriumReserve0, p.equilibriumReserve1, p.concentrationX);
-            if (newReserve1 >= fxMid) {
-                xMax = xMid;
-            } else {
-                xMin = xMid + 1;
-            }
-        }
-        if (newReserve1 < f(xMin, p.priceX, p.priceY, p.equilibriumReserve0, p.equilibriumReserve1, p.concentrationX)) {
-            xMin += 1;
-        }
-        return xMin;
-    }
-
-    /// @dev EulerSwap derivative helper function to find the price after a swap
-    /// Pre-conditions: 0 < x <= x0, 1 <= {px,py} <= 1e36, {x0,y0} <= type(uint112).max, c <= 1e18
-    function df_dx(uint256 x, uint256 px, uint256 py, uint256 x0, uint256 y0, uint256 c)
-        internal
-        pure
-        returns (int256)
-    {
-        uint256 r = Math.mulDiv(x0 * x0 / x, 1e18, x, Math.Rounding.Ceil);
-        return -int256(px * (c + (1e18 - c) * r / 1e18) / py);
-    }
 }

test/CurveLib.t.sol

@@ -32,7 +32,7 @@ contract CurveLibTest is EulerSwapTestBase {
 
     function test_fuzzfInverse(uint256 x, uint256 px, uint256 py, uint256 x0, uint256 y0, uint256 cx, uint256 cy)
         public
-        view
+        pure
     {
         // Params
         px = 1e18;
@@ -72,7 +72,7 @@ contract CurveLibTest is EulerSwapTestBase {
         uint256 xCalc = CurveLib.fInverse(y, px, py, x0, y0, cx);
         console.log("xCalc", xCalc);
         uint256 yCalc = CurveLib.f(xCalc, px, py, x0, y0, cx);
-        uint256 xBin = CurveLib.binarySearch(p, y, 1, x0);
+        uint256 xBin = binarySearch(p, y, 1, x0);
         uint256 yBin = CurveLib.f(xBin, px, py, x0, y0, cx);
         console.log("x    ", x);
         console.log("xCalc", xCalc);
@@ -86,4 +86,32 @@ contract CurveLibTest is EulerSwapTestBase {
             assert(int256(xCalc) - int256(xBin) <= 3 || int256(yCalc) - int256(yBin) <= 3); // suspect this is 2 wei error in fInverse() + 1 wei error in f()
         }
     }
+
+    /// @dev Less efficient method to compute fInverse. Useful for differential fuzzing.
+    function binarySearch(IEulerSwap.Params memory p, uint256 newReserve1, uint256 xMin, uint256 xMax)
+        internal
+        pure
+        returns (uint256)
+    {
+        if (xMin < 1) {
+            xMin = 1;
+        }
+        while (xMin < xMax) {
+            uint256 xMid = (xMin + xMax) / 2;
+            uint256 fxMid =
+                CurveLib.f(xMid, p.priceX, p.priceY, p.equilibriumReserve0, p.equilibriumReserve1, p.concentrationX);
+            if (newReserve1 >= fxMid) {
+                xMax = xMid;
+            } else {
+                xMin = xMid + 1;
+            }
+        }
+        if (
+            newReserve1
+                < CurveLib.f(xMin, p.priceX, p.priceY, p.equilibriumReserve0, p.equilibriumReserve1, p.concentrationX)
+        ) {
+            xMin += 1;
+        }
+        return xMin;
+    }
 }