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Some minor optimizations and refactors (#337)
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* Some minor optimizations and refactors

* Fix comments

* Fix comments

* Add comments

* Add comments

* Add comments

* Refactor

* Inline transfer

* Fix test typo

* Rename back to _boolToUint256

* Shift transferFrom to minimize diff

* Add comments on nested ifs
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@Vectorized
Vectorized authored Jun 14, 2022
1 parent d31f52f commit 3fed4e9
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109 changes: 63 additions & 46 deletions contracts/ERC721A.sol
View file
Original file line number Diff line number Diff line change
Expand Up @@ -282,12 +282,12 @@ contract ERC721A is IERC721A {
/**
* @dev Packs ownership data into a single uint256.
*/
function _packOwnershipData(address owner, uint256 flags) private view returns (uint256 value) {
function _packOwnershipData(address owner, uint256 flags) private view returns (uint256 result) {
assembly {
// Mask `owner` to the lower 160 bits, in case the upper bits somehow aren't clean.
owner := and(owner, BITMASK_ADDRESS)
// `owner | (block.timestamp << BITPOS_START_TIMESTAMP) | flags`.
value := or(owner, or(shl(BITPOS_START_TIMESTAMP, timestamp()), flags))
result := or(owner, or(shl(BITPOS_START_TIMESTAMP, timestamp()), flags))
}
}

Expand Down Expand Up @@ -381,17 +381,6 @@ contract ERC721A is IERC721A {
return _operatorApprovals[owner][operator];
}

/**
* @dev See {IERC721-transferFrom}.
*/
function transferFrom(
address from,
address to,
uint256 tokenId
) public virtual override {
_transfer(from, to, tokenId);
}

/**
* @dev See {IERC721-safeTransferFrom}.
*/
Expand All @@ -412,7 +401,7 @@ contract ERC721A is IERC721A {
uint256 tokenId,
bytes memory _data
) public virtual override {
_transfer(from, to, tokenId);
transferFrom(from, to, tokenId);
if (to.code.length != 0)
if (!_checkContractOnERC721Received(from, to, tokenId, _data)) {
revert TransferToNonERC721ReceiverImplementer();
Expand Down Expand Up @@ -493,14 +482,14 @@ contract ERC721A is IERC721A {
_beforeTokenTransfers(address(0), to, startTokenId, quantity);

// Overflows are incredibly unrealistic.
// balance or numberMinted overflow if current value of either + quantity > 1.8e19 (2**64) - 1
// updatedIndex overflows if _currentIndex + quantity > 1.2e77 (2**256) - 1
// `balance` and `numberMinted` have a maximum limit of 2**64.
// `tokenId` has a maximum limit of 2**256.
unchecked {
// Updates:
// - `balance += quantity`.
// - `numberMinted += quantity`.
//
// We can directly add to the balance and number minted.
// We can directly add to the `balance` and `numberMinted`.
_packedAddressData[to] += quantity * ((1 << BITPOS_NUMBER_MINTED) | 1);

// Updates:
Expand All @@ -513,11 +502,11 @@ contract ERC721A is IERC721A {
(_boolToUint256(quantity == 1) << BITPOS_NEXT_INITIALIZED) | _nextExtraData(address(0), to, 0)
);

uint256 offset = startTokenId;
uint256 tokenId = startTokenId;
uint256 end = quantity + startTokenId;
do {
emit Transfer(address(0), to, offset++);
} while (offset < end);
emit Transfer(address(0), to, tokenId++);
} while (tokenId < end);

_currentIndex = startTokenId + quantity;
}
Expand Down Expand Up @@ -559,7 +548,7 @@ contract ERC721A is IERC721A {
// - `balance += quantity`.
// - `numberMinted += quantity`.
//
// We can directly add to the balance and number minted.
// We can directly add to the `balance` and `numberMinted`.
_packedAddressData[to] += quantity * ((1 << BITPOS_NUMBER_MINTED) | 1);

// Updates:
Expand All @@ -580,15 +569,40 @@ contract ERC721A is IERC721A {
}

/**
* @dev Zeroes out _tokenApprovals[tokenId]
* @dev Returns the storage slot and value for the approved address of `tokenId`.
*/
function _removeTokenApproval(uint256 tokenId) private {
mapping(uint256 => address) storage tokenApprovalPtr = _tokenApprovals;
function _getApprovedAddress(uint256 tokenId)
private
view
returns (uint256 approvedAddressSlot, address approvedAddress)
{
mapping(uint256 => address) storage tokenApprovalsPtr = _tokenApprovals;
// The following is equivalent to `approvedAddress = _tokenApprovals[tokenId]`.
assembly {
// Compute the slot.
mstore(0x00, tokenId)
mstore(0x20, tokenApprovalPtr.slot)
let hash := keccak256(0, 0x40)
sstore(hash, 0)
mstore(0x20, tokenApprovalsPtr.slot)
approvedAddressSlot := keccak256(0x00, 0x40)
// Load the slot's value from storage.
approvedAddress := sload(approvedAddressSlot)
}
}

/**
* @dev Returns whether the `approvedAddress` is equals to `from` or `msgSender`.
*/
function _isOwnerOrApproved(
address approvedAddress,
address from,
address msgSender
) private pure returns (bool result) {
assembly {
// Mask `from` to the lower 160 bits, in case the upper bits somehow aren't clean.
from := and(from, BITMASK_ADDRESS)
// Mask `msgSender` to the lower 160 bits, in case the upper bits somehow aren't clean.
msgSender := and(msgSender, BITMASK_ADDRESS)
// `msgSender == from || msgSender == approvedAddress`.
result := or(eq(msgSender, from), eq(msgSender, approvedAddress))
}
}

Expand All @@ -602,29 +616,31 @@ contract ERC721A is IERC721A {
*
* Emits a {Transfer} event.
*/
function _transfer(
function transferFrom(
address from,
address to,
uint256 tokenId
) private {
) public virtual override {
uint256 prevOwnershipPacked = _packedOwnershipOf(tokenId);

if (address(uint160(prevOwnershipPacked)) != from) revert TransferFromIncorrectOwner();

address approvedAddress = _tokenApprovals[tokenId];
(uint256 approvedAddressSlot, address approvedAddress) = _getApprovedAddress(tokenId);

bool isApprovedOrOwner = (_msgSenderERC721A() == from ||
isApprovedForAll(from, _msgSenderERC721A()) ||
approvedAddress == _msgSenderERC721A());
// The nested ifs save around 20+ gas over a compound boolean condition.
if (!_isOwnerOrApproved(approvedAddress, from, _msgSenderERC721A()))
if (!isApprovedForAll(from, _msgSenderERC721A())) revert TransferCallerNotOwnerNorApproved();

if (!isApprovedOrOwner) revert TransferCallerNotOwnerNorApproved();
if (to == address(0)) revert TransferToZeroAddress();

_beforeTokenTransfers(from, to, tokenId, 1);

// Clear approvals from the previous owner.
if (approvedAddress != address(0)) {
_removeTokenApproval(tokenId);
assembly {
if approvedAddress {
// This is equivalent to `delete _tokenApprovals[tokenId]`.
sstore(approvedAddressSlot, 0)
}
}

// Underflow of the sender's balance is impossible because we check for
Expand Down Expand Up @@ -684,26 +700,27 @@ contract ERC721A is IERC721A {
uint256 prevOwnershipPacked = _packedOwnershipOf(tokenId);

address from = address(uint160(prevOwnershipPacked));
address approvedAddress = _tokenApprovals[tokenId];

if (approvalCheck) {
bool isApprovedOrOwner = (_msgSenderERC721A() == from ||
isApprovedForAll(from, _msgSenderERC721A()) ||
approvedAddress == _msgSenderERC721A());
(uint256 approvedAddressSlot, address approvedAddress) = _getApprovedAddress(tokenId);

if (!isApprovedOrOwner) revert TransferCallerNotOwnerNorApproved();
}
if (approvalCheck)
// The nested ifs save around 20+ gas over a compound boolean condition.
if (!_isOwnerOrApproved(approvedAddress, from, _msgSenderERC721A()))
if (!isApprovedForAll(from, _msgSenderERC721A())) revert TransferCallerNotOwnerNorApproved();

_beforeTokenTransfers(from, address(0), tokenId, 1);

// Clear approvals from the previous owner.
if (approvedAddress != address(0)) {
_removeTokenApproval(tokenId);
assembly {
if approvedAddress {
// This is equivalent to `delete _tokenApprovals[tokenId]`.
sstore(approvedAddressSlot, 0)
}
}

// Underflow of the sender's balance is impossible because we check for
// ownership above and the recipient's balance can't realistically overflow.
// Counter overflow is incredibly unrealistic as tokenId would have to be 2**256.
// Counter overflow is incredibly unrealistic as `tokenId` would have to be 2**256.
unchecked {
// Updates:
// - `balance -= 1`.
Expand Down
2 changes: 1 addition & 1 deletion test/ERC721A.test.js
View file
Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,7 @@ const createTestSuite = ({ contract, constructorArgs }) =>

describe('tokenURI (ERC721Metadata)', async function () {
describe('tokenURI', async function () {
it('sends an emtpy uri by default', async function () {
it('sends an empty uri by default', async function () {
expect(await this.erc721a.tokenURI(offsetted(0))).to.eq('');
});

Expand Down

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