🥢 Nit bytes4 return value comments (#860)

Author: Vectorized

.gas-snapshot

@@ -221,21 +221,21 @@ ERC2981Test:testRoyaltyOverflowCheckDifferential(uint256,uint256) (runs: 257, μ
 ERC2981Test:testSetAndGetRoyaltyInfo(uint256) (runs: 257, μ: 108094, ~: 104814)
 ERC2981Test:test__codesize() (gas: 8418)
 ERC4337FactoryTest:testCreateAccountRepeatedDeployment() (gas: 149757)
-ERC4337FactoryTest:testCreateAccountRepeatedDeployment(uint256) (runs: 257, μ: 171752, ~: 171609)
-ERC4337FactoryTest:testDeployDeterministic(uint256) (runs: 257, μ: 133652, ~: 139899)
+ERC4337FactoryTest:testCreateAccountRepeatedDeployment(uint256) (runs: 257, μ: 171763, ~: 171617)
+ERC4337FactoryTest:testDeployDeterministic(uint256) (runs: 257, μ: 133674, ~: 139900)
 ERC4337FactoryTest:test__codesize() (gas: 13258)
 ERC4337Test:testCdFallback() (gas: 433020)
 ERC4337Test:testCdFallback2() (gas: 1129634)
 ERC4337Test:testDelegateExecute() (gas: 369570)
-ERC4337Test:testDelegateExecute(uint256) (runs: 257, μ: 354025, ~: 344555)
+ERC4337Test:testDelegateExecute(uint256) (runs: 257, μ: 353354, ~: 344555)
 ERC4337Test:testDelegateExecuteRevertsIfOwnerSlotValueChanged() (gas: 319282)
 ERC4337Test:testDepositFunctions() (gas: 491986)
 ERC4337Test:testDirectStorage() (gas: 70413)
 ERC4337Test:testDisableInitializerForImplementation() (gas: 1169310)
 ERC4337Test:testETHReceived() (gas: 16584)
 ERC4337Test:testExecute() (gas: 382786)
 ERC4337Test:testExecuteBatch() (gas: 692649)
-ERC4337Test:testExecuteBatch(uint256) (runs: 257, μ: 513716, ~: 368276)
+ERC4337Test:testExecuteBatch(uint256) (runs: 257, μ: 499791, ~: 368276)
 ERC4337Test:testInitializer() (gas: 285192)
 ERC4337Test:testIsValidSignature() (gas: 111663)
 ERC4337Test:testIsValidSignaturePersonalSign() (gas: 96270)
@@ -266,19 +266,19 @@ ERC4626Test:testWithdrawWithNotEnoughUnderlyingAmountReverts() (gas: 144074)
 ERC4626Test:testWithdrawZero() (gas: 52807)
 ERC4626Test:test__codesize() (gas: 39940)
 ERC6551Test:testCdFallback() (gas: 894305)
-ERC6551Test:testDeployERC6551(uint256) (runs: 257, μ: 171305, ~: 168789)
+ERC6551Test:testDeployERC6551(uint256) (runs: 257, μ: 171193, ~: 168789)
 ERC6551Test:testDeployERC6551Proxy() (gas: 80351)
 ERC6551Test:testExecute() (gas: 507899)
 ERC6551Test:testExecuteBatch() (gas: 817000)
-ERC6551Test:testExecuteBatch(uint256) (runs: 257, μ: 630373, ~: 761641)
+ERC6551Test:testExecuteBatch(uint256) (runs: 257, μ: 627737, ~: 586245)
 ERC6551Test:testInitializeERC6551ProxyImplementation() (gas: 189796)
 ERC6551Test:testIsValidSignature() (gas: 187642)
-ERC6551Test:testIsValidSigner(address) (runs: 257, μ: 167305, ~: 167323)
+ERC6551Test:testIsValidSigner(address) (runs: 257, μ: 167326, ~: 167324)
 ERC6551Test:testOnERC1155BatchReceived() (gas: 1526537)
 ERC6551Test:testOnERC1155Received() (gas: 1523871)
 ERC6551Test:testOnERC721Received() (gas: 1501317)
 ERC6551Test:testOnERC721ReceivedCycles() (gas: 1713680)
-ERC6551Test:testOnERC721ReceivedCyclesWithDifferentChainIds(uint256) (runs: 257, μ: 448984, ~: 454608)
+ERC6551Test:testOnERC721ReceivedCyclesWithDifferentChainIds(uint256) (runs: 257, μ: 448971, ~: 454680)
 ERC6551Test:testSupportsInterface() (gas: 169367)
 ERC6551Test:testUpgrade() (gas: 1165638)
 ERC6551Test:test__codesize() (gas: 47524)

src/accounts/ERC1271.sol

@@ -98,6 +98,7 @@ abstract contract ERC1271 is EIP712 {
         /// @solidity memory-safe-assembly
         assembly {
             // `success ? bytes4(keccak256("isValidSignature(bytes32,bytes)")) : 0xffffffff`.
+            // We use `0xffffffff` for invalid, in convention with the reference implementation.
             result := shl(224, or(0x1626ba7e, sub(0, iszero(success))))
         }
     }

src/accounts/ERC6551.sol

@@ -132,7 +132,7 @@ abstract contract ERC6551 is UUPSUpgradeable, Receiver, ERC1271 {
         bool isValid = _isValidSigner(signer);
         /// @solidity memory-safe-assembly
         assembly {
-            // `success ? bytes4(keccak256("isValidSigner(address,bytes)")) : 0x00000000`.
+            // `isValid ? bytes4(keccak256("isValidSigner(address,bytes)")) : 0x00000000`.
             // We use `0x00000000` for invalid, in convention with the reference implementation.
             result := shl(224, mul(0x523e3260, iszero(iszero(isValid))))
         }