remove OZ dependency

.gitmodules

@@ -1,7 +1,3 @@
 [submodule "lib/forge-std"]
 	path = lib/forge-std
 	url = https://github.com/foundry-rs/forge-std
-[submodule "lib/openzeppelin-contracts-upgradeable"]
-	path = lib/openzeppelin-contracts-upgradeable
-	url = https://github.com/openzeppelin/openzeppelin-contracts-upgradeable
-	branch = v5.0.2

remappings.txt

@@ -1,2 +1 @@
 forge-std/=lib/forge-std/src/
-openzeppelin-upgradeable/=lib/openzeppelin-contracts-upgradeable/contracts/

src/math/SVI.sol

@@ -6,8 +6,6 @@ import "src/decimals/SignedDecimalMath.sol";
 import "src/decimals/DecimalMath.sol";
 import "./FixedPointMathLib.sol";
 
-import "openzeppelin-upgradeable/utils/math/SafeCastUpgradeable.sol";
-
 /**
  * @title SVI
  * @author Lyra
@@ -18,8 +16,6 @@ library SVI {
   using SignedDecimalMath for int;
   using FixedPointMathLib for uint;
   using FixedPointMathLib for int;
-  using SafeCastUpgradeable for int;
-  using SafeCastUpgradeable for uint;
 
   error SVI_InvalidParameters();
   error SVI_NoForwardPrice();
@@ -81,7 +77,7 @@ library SVI {
    */
   function getK(uint strike, int a, uint b, uint sigma, uint forwardPrice) internal pure returns (int k) {
     // calculate the bounds
-    int volFactor = int(FixedPointMathLib.sqrt((a + b.multiplyDecimal(sigma).toInt256()).toUint256()));
+    int volFactor = int(FixedPointMathLib.sqrt(toUintSafe(a + toIntSafe(b.multiplyDecimal(sigma)))));
     int k_bound = volFactor.multiplyDecimal(TOTAL_VOL_SCALAR);
     int sk = int(strike.divideDecimal(forwardPrice));
 
@@ -94,4 +90,14 @@ library SVI {
     if (k > k_bound) return k_bound;
     if (k < -k_bound) return -k_bound;
   }
+
+  function toIntSafe(uint value) internal pure returns (int) {
+    if (int(value) < 0) revert("SVI: invalid uint cast");
+    return int(value);
+  }
+
+  function toUintSafe(int value) internal pure returns (uint) {
+    if (value < 0) revert("SVI: value must be positive");
+    return uint(value);
+  }
 }

test/math/SVI.t.sol

@@ -116,7 +116,7 @@ contract SVITest is Test {
       sigma: 0.000410958904109589e18,
       forwardPrice: 1800e18
     });
-    vm.expectRevert(bytes("SafeCast: value must be positive"));
+    vm.expectRevert(bytes("SVI: value must be positive"));
     tester.getVol(1800e18, params);
   }