Optimize array allocation in ERC1155

.changeset/serious-books-lie.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`ERC1155`: Optimize array allocation.

contracts/token/ERC1155/ERC1155.sol

@@ -206,8 +206,7 @@ contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
     function _safeTransferFrom(address from, address to, uint256 id, uint256 amount, bytes memory data) internal {
         require(to != address(0), "ERC1155: transfer to the zero address");
         require(from != address(0), "ERC1155: transfer from the zero address");
-        uint256[] memory ids = _asSingletonArray(id);
-        uint256[] memory amounts = _asSingletonArray(amount);
+        (uint256[] memory ids, uint256[] memory amounts) = _asSingletonArrays(id, amount);
         _update(from, to, ids, amounts, data);
     }
 
@@ -269,8 +268,7 @@ contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
      */
     function _mint(address to, uint256 id, uint256 amount, bytes memory data) internal {
         require(to != address(0), "ERC1155: mint to the zero address");
-        uint256[] memory ids = _asSingletonArray(id);
-        uint256[] memory amounts = _asSingletonArray(amount);
+        (uint256[] memory ids, uint256[] memory amounts) = _asSingletonArrays(id, amount);
         _update(address(0), to, ids, amounts, data);
     }
 
@@ -302,8 +300,7 @@ contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
      */
     function _burn(address from, uint256 id, uint256 amount) internal {
         require(from != address(0), "ERC1155: burn from the zero address");
-        uint256[] memory ids = _asSingletonArray(id);
-        uint256[] memory amounts = _asSingletonArray(amount);
+        (uint256[] memory ids, uint256[] memory amounts) = _asSingletonArrays(id, amount);
         _update(from, address(0), ids, amounts, "");
     }
 
@@ -376,10 +373,21 @@ contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
         }
     }
 
-    function _asSingletonArray(uint256 element) private pure returns (uint256[] memory) {
-        uint256[] memory array = new uint256[](1);
-        array[0] = element;
-
-        return array;
+    function _asSingletonArrays(
+        uint256 element1,
+        uint256 element2
+    ) private pure returns (uint256[] memory array1, uint256[] memory array2) {
+        /// @solidity memory-safe-assembly
+        assembly {
+            array1 := mload(0x40)
+            mstore(array1, 1)
+            mstore(add(array1, 0x20), element1)
+
+            array2 := add(array1, 0x40)
+            mstore(array2, 1)
+            mstore(add(array2, 0x20), element2)
+
+            mstore(0x40, add(array2, 0x40))
+        }
     }
 }