Optimize array allocation in ERC1155 (#4196)

Co-authored-by: Francisco <fg@frang.io>

.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))
+ }
  }
 }