feat: add G3MStrategyLib, computeInvariant

contracts/strategies/G3MStrategyLib.sol

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+pragma solidity ^0.8.18;
+
+import "solmate/utils/FixedPointMathLib.sol";
+
+using FixedPointMathLib for uint256;
+using FixedPointMathLib for int256;
+
+library G3MStrategyLib {
+    /**
+     * @dev Computes the invariant of the pool (rounding down) using the
+     * following formula:
+     *
+     *        ⎛  wX⎞   ⎛  wY⎞
+     *    k = ⎝rX  ⎠ ⋅ ⎝rY  ⎠
+     *
+     * @param reserveX Reserve of token X
+     * @param weightX Weight of token X
+     * @param reserveY Reserve of token Y
+     * @param weightY Weight of token Y
+     * @return k Invariant of the pool
+     */
+    function computeInvariant(
+        uint256 reserveX,
+        uint256 weightX,
+        uint256 reserveY,
+        uint256 weightY
+    ) internal pure returns (uint256 k) {
+        k = uint256(
+            uint256(int256(reserveX).powWad(int256(weightX))).mulWadDown(
+                uint256(int256(reserveY).powWad(int256(weightY)))
+            )
+        );
+    }
+}