From d65f1581f0224d1f6caf69de271153766a23ca32 Mon Sep 17 00:00:00 2001
From: Alice <34962750+hensha256@users.noreply.github.com>
Date: Sun, 4 Aug 2024 16:38:15 +0100
Subject: [PATCH] Optimise permit hashing (#260)

* permit hash in assembly

* fuzz test
---
 .forge-snapshots/PositionManager_permit.snap    |  2 +-
 .../PositionManager_permit_secondPosition.snap  |  2 +-
 .../PositionManager_permit_twice.snap           |  2 +-
 src/libraries/ERC721PermitHash.sol              | 17 +++++++++++++++--
 test/ERC721Permit.t.sol                         |  6 ++++++
 5 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/.forge-snapshots/PositionManager_permit.snap b/.forge-snapshots/PositionManager_permit.snap
index b2faa7cc..dfab40b6 100644
--- a/.forge-snapshots/PositionManager_permit.snap
+++ b/.forge-snapshots/PositionManager_permit.snap
@@ -1 +1 @@
-79585
\ No newline at end of file
+79486
\ No newline at end of file
diff --git a/.forge-snapshots/PositionManager_permit_secondPosition.snap b/.forge-snapshots/PositionManager_permit_secondPosition.snap
index 60f10b03..19350c74 100644
--- a/.forge-snapshots/PositionManager_permit_secondPosition.snap
+++ b/.forge-snapshots/PositionManager_permit_secondPosition.snap
@@ -1 +1 @@
-62497
\ No newline at end of file
+62398
\ No newline at end of file
diff --git a/.forge-snapshots/PositionManager_permit_twice.snap b/.forge-snapshots/PositionManager_permit_twice.snap
index 3df69310..ecadddb0 100644
--- a/.forge-snapshots/PositionManager_permit_twice.snap
+++ b/.forge-snapshots/PositionManager_permit_twice.snap
@@ -1 +1 @@
-45397
\ No newline at end of file
+45298
\ No newline at end of file
diff --git a/src/libraries/ERC721PermitHash.sol b/src/libraries/ERC721PermitHash.sol
index cf4c74f0..9a36d6de 100644
--- a/src/libraries/ERC721PermitHash.sol
+++ b/src/libraries/ERC721PermitHash.sol
@@ -5,7 +5,20 @@ library ERC721PermitHashLibrary {
     /// @dev Value is equal to keccak256("Permit(address spender,uint256 tokenId,uint256 nonce,uint256 deadline)");
     bytes32 constant PERMIT_TYPEHASH = 0x49ecf333e5b8c95c40fdafc95c1ad136e8914a8fb55e9dc8bb01eaa83a2df9ad;
 
-    function hash(address spender, uint256 tokenId, uint256 nonce, uint256 deadline) internal pure returns (bytes32) {
-        return keccak256(abi.encode(PERMIT_TYPEHASH, spender, tokenId, nonce, deadline));
+    function hash(address spender, uint256 tokenId, uint256 nonce, uint256 deadline)
+        internal
+        pure
+        returns (bytes32 digest)
+    {
+        // equivalent to: keccak256(abi.encode(PERMIT_TYPEHASH, spender, tokenId, nonce, deadline));
+        assembly ("memory-safe") {
+            let fmp := mload(0x40)
+            mstore(fmp, PERMIT_TYPEHASH)
+            mstore(add(fmp, 0x20), spender)
+            mstore(add(fmp, 0x40), tokenId)
+            mstore(add(fmp, 0x60), nonce)
+            mstore(add(fmp, 0x80), deadline)
+            digest := keccak256(fmp, 0xa0)
+        }
     }
 }
diff --git a/test/ERC721Permit.t.sol b/test/ERC721Permit.t.sol
index d7126223..16f4f39f 100644
--- a/test/ERC721Permit.t.sol
+++ b/test/ERC721Permit.t.sol
@@ -67,6 +67,12 @@ contract ERC721PermitTest is Test {
         );
     }
 
+    function test_fuzz_permitHash(address spender, uint256 tokenId, uint256 nonce, uint256 deadline) public view {
+        bytes32 expectedHash =
+            keccak256(abi.encode(ERC721PermitHashLibrary.PERMIT_TYPEHASH, spender, tokenId, nonce, deadline));
+        assertEq(expectedHash, ERC721PermitHashLibrary.hash(spender, tokenId, nonce, deadline));
+    }
+
     function test_domainSeparator() public view {
         assertEq(
             IERC721Permit(address(erc721Permit)).DOMAIN_SEPARATOR(),