Paymaster gas optimization

.changeset/paymaster-gas-council.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`PaymasterSigner`, `PaymasterERC20`, `PaymasterERC721Owner`: Reduce gas usage on the validation and postOp hot paths.

contracts/account/paymaster/extensions/PaymasterERC20.sol

@@ -205,8 +205,11 @@ abstract contract PaymasterERC20 is Paymaster {
         bytes calldata /* prefundContext */
     ) internal virtual returns (bool success, uint256 actualAmount) {
         // Under ERC-4337 EntryPoint, `actualGasCost <= maxCost` and `actualUserOpFeePerGas <= maxFeePerGas`,
-        // so `actualAmount_ <= prefundAmount` holds.
-        return (token.trySafeTransfer(prefunder, prefundAmount - actualAmount_), actualAmount_);
+        // so `actualAmount_ <= prefundAmount` holds and the subtraction cannot underflow. If a caller breaks
+        // that requirement, the wrapped amount makes `trySafeTransfer` fail and {_postOp} revert.
+        unchecked {
+            return (token.trySafeTransfer(prefunder, prefundAmount - actualAmount_), actualAmount_);
+        }
     }
 
     /**
@@ -289,9 +292,12 @@ abstract contract PaymasterERC20 is Paymaster {
      */
     function _erc20Cost(uint256 nativeCost, uint256 tokenPerNative) internal view virtual returns (uint256) {
         uint256 denominator = _tokenPerNativeDenominator();
-        (uint256 high, ) = nativeCost.mul512(tokenPerNative);
+        (uint256 high, uint256 low) = nativeCost.mul512(tokenPerNative);
+        if (high >= denominator) return type(uint256).max;
+        // When the product fits in one word, a plain ceiling division avoids repeating
+        // the 512-bit product inside `mulDiv`.
         return
-            high < denominator ? nativeCost.mulDiv(tokenPerNative, denominator, Math.Rounding.Ceil) : type(uint256).max;
+            high == 0 ? low.ceilDiv(denominator) : nativeCost.mulDiv(tokenPerNative, denominator, Math.Rounding.Ceil);
     }
 
     /// @dev Internal function that allows the withdrawer to extract ERC-20 tokens resulting from gas payments.

contracts/account/paymaster/extensions/PaymasterERC721Owner.sol

@@ -4,6 +4,7 @@ pragma solidity ^0.8.20;
 
 import {IERC721} from "../../../interfaces/IERC721.sol";
 import {ERC4337Utils, PackedUserOperation} from "../../utils/ERC4337Utils.sol";
+import {SafeCast} from "../../../utils/math/SafeCast.sol";
 import {Paymaster} from "../Paymaster.sol";
 
 /**
@@ -44,10 +45,9 @@ abstract contract PaymasterERC721Owner is Paymaster {
         return (
             bytes(""),
             // balanceOf reverts if the `userOp.sender` is the address(0), so this becomes unreachable with address(0)
-            // assuming a compliant entrypoint (`_validatePaymasterUserOp` is called after `validateUserOp`),
-            token().balanceOf(userOp.sender) == 0
-                ? ERC4337Utils.SIG_VALIDATION_FAILED
-                : ERC4337Utils.SIG_VALIDATION_SUCCESS
+            // assuming a compliant entrypoint (`_validatePaymasterUserOp` is called after `validateUserOp`).
+            // `SIG_VALIDATION_FAILED == 1` and `SIG_VALIDATION_SUCCESS == 0`, so the cast is branchless.
+            SafeCast.toUint(token().balanceOf(userOp.sender) == 0)
         );
     }
 }

contracts/account/paymaster/extensions/PaymasterSigner.sol

@@ -37,6 +37,11 @@ abstract contract PaymasterSigner is AbstractSigner, EIP712, Paymaster {
         uint48 validAfter,
         uint48 validUntil
     ) internal view virtual returns (bytes32) {
+        // Both paymaster gas limits share the word at [20:52]: a single load replaces
+        // the two `ERC4337Utils` accessors, which each length-check and load it.
+        uint256 paymasterGasLimits = userOp.paymasterAndData.length < 52
+            ? 0
+            : uint256(bytes32(userOp.paymasterAndData[20:52]));
         return
             _hashTypedDataV4(
                 keccak256(
@@ -49,8 +54,8 @@ abstract contract PaymasterSigner is AbstractSigner, EIP712, Paymaster {
                         userOp.accountGasLimits,
                         userOp.preVerificationGas,
                         userOp.gasFees,
-                        userOp.paymasterVerificationGasLimit(),
-                        userOp.paymasterPostOpGasLimit(),
+                        paymasterGasLimits >> 128,
+                        uint256(uint128(paymasterGasLimits)),
                         validAfter,
                         validUntil
                     )
@@ -89,9 +94,11 @@ abstract contract PaymasterSigner is AbstractSigner, EIP712, Paymaster {
         PackedUserOperation calldata userOp
     ) internal pure virtual returns (uint48 validAfter, uint48 validUntil, bytes calldata signature) {
         bytes calldata paymasterData = userOp.paymasterData();
-        return
-            paymasterData.length < 12
-                ? (uint48(0), uint48(0), Calldata.emptyBytes())
-                : (uint48(bytes6(paymasterData[0:6])), uint48(bytes6(paymasterData[6:12])), paymasterData[12:]);
+        if (paymasterData.length < 12) return (uint48(0), uint48(0), Calldata.emptyBytes());
+
+        // Both timestamps share the 12-byte window at [0:12]: a single load replaces
+        // the two bounds-checked slices.
+        bytes12 validity = bytes12(paymasterData[:12]);
+        return (uint48(bytes6(validity)), uint48(bytes6(validity << 48)), paymasterData[12:]);
     }
 }