// SPDX-License-Identifier: MIT// OpenZeppelin Contracts (last updated v4.5.0) (utils/Address.sol)pragmasolidity ^0.8.1;/**
* @dev Collection of functions related to the address type
*/libraryAddress{
/**
* @dev Returns true if `account` is a contract.
*
* [IMPORTANT]
* ====
* It is unsafe to assume that an address for which this function returns
* false is an externally-owned account (EOA) and not a contract.
*
* Among others, `isContract` will return false for the following
* types of addresses:
*
* - an externally-owned account
* - a contract in construction
* - an address where a contract will be created
* - an address where a contract lived, but was destroyed
* ====
*
* [IMPORTANT]
* ====
* You shouldn't rely on `isContract` to protect against flash loan attacks!
*
* Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
* like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
* constructor.
* ====
*/functionisContract(address account) internalviewreturns (bool) {
// This method relies on extcodesize/address.code.length, which returns 0// for contracts in construction, since the code is only stored at the end// of the constructor execution.return account.code.length>0;
}
/**
* @dev Replacement for Solidity's `transfer`: sends `amount` wei to
* `recipient`, forwarding all available gas and reverting on errors.
*
* https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
* of certain opcodes, possibly making contracts go over the 2300 gas limit
* imposed by `transfer`, making them unable to receive funds via
* `transfer`. {sendValue} removes this limitation.
*
* https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
*
* IMPORTANT: because control is transferred to `recipient`, care must be
* taken to not create reentrancy vulnerabilities. Consider using
* {ReentrancyGuard} or the
* https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
*/functionsendValue(addresspayable recipient, uint256 amount) internal{
require(address(this).balance>= amount, "Address: insufficient balance");
(bool success, ) = recipient.call{value: amount}("");
require(success, "Address: unable to send value, recipient may have reverted");
}
/**
* @dev Performs a Solidity function call using a low level `call`. A
* plain `call` is an unsafe replacement for a function call: use this
* function instead.
*
* If `target` reverts with a revert reason, it is bubbled up by this
* function (like regular Solidity function calls).
*
* Returns the raw returned data. To convert to the expected return value,
* use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
*
* Requirements:
*
* - `target` must be a contract.
* - calling `target` with `data` must not revert.
*
* _Available since v3.1._
*/functionfunctionCall(address target, bytesmemory data) internalreturns (bytesmemory) {
return functionCall(target, data, "Address: low-level call failed");
}
/**
* @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
* `errorMessage` as a fallback revert reason when `target` reverts.
*
* _Available since v3.1._
*/functionfunctionCall(address target,
bytesmemory data,
stringmemory errorMessage
) internalreturns (bytesmemory) {
return functionCallWithValue(target, data, 0, errorMessage);
}
/**
* @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
* but also transferring `value` wei to `target`.
*
* Requirements:
*
* - the calling contract must have an ETH balance of at least `value`.
* - the called Solidity function must be `payable`.
*
* _Available since v3.1._
*/functionfunctionCallWithValue(address target,
bytesmemory data,
uint256 value
) internalreturns (bytesmemory) {
return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
}
/**
* @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
* with `errorMessage` as a fallback revert reason when `target` reverts.
*
* _Available since v3.1._
*/functionfunctionCallWithValue(address target,
bytesmemory data,
uint256 value,
stringmemory errorMessage
) internalreturns (bytesmemory) {
require(address(this).balance>= value, "Address: insufficient balance for call");
require(isContract(target), "Address: call to non-contract");
(bool success, bytesmemory returndata) = target.call{value: value}(data);
return verifyCallResult(success, returndata, errorMessage);
}
/**
* @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
* but performing a static call.
*
* _Available since v3.3._
*/functionfunctionStaticCall(address target, bytesmemory data) internalviewreturns (bytesmemory) {
return functionStaticCall(target, data, "Address: low-level static call failed");
}
/**
* @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
* but performing a static call.
*
* _Available since v3.3._
*/functionfunctionStaticCall(address target,
bytesmemory data,
stringmemory errorMessage
) internalviewreturns (bytesmemory) {
require(isContract(target), "Address: static call to non-contract");
(bool success, bytesmemory returndata) = target.staticcall(data);
return verifyCallResult(success, returndata, errorMessage);
}
/**
* @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
* but performing a delegate call.
*
* _Available since v3.4._
*/functionfunctionDelegateCall(address target, bytesmemory data) internalreturns (bytesmemory) {
return functionDelegateCall(target, data, "Address: low-level delegate call failed");
}
/**
* @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
* but performing a delegate call.
*
* _Available since v3.4._
*/functionfunctionDelegateCall(address target,
bytesmemory data,
stringmemory errorMessage
) internalreturns (bytesmemory) {
require(isContract(target), "Address: delegate call to non-contract");
(bool success, bytesmemory returndata) = target.delegatecall(data);
return verifyCallResult(success, returndata, errorMessage);
}
/**
* @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
* revert reason using the provided one.
*
* _Available since v4.3._
*/functionverifyCallResult(bool success,
bytesmemory returndata,
stringmemory errorMessage
) internalpurereturns (bytesmemory) {
if (success) {
return returndata;
} else {
// Look for revert reason and bubble it up if presentif (returndata.length>0) {
// The easiest way to bubble the revert reason is using memory via assemblyassembly {
let returndata_size :=mload(returndata)
revert(add(32, returndata), returndata_size)
}
} else {
revert(errorMessage);
}
}
}
}
Contract Source Code
File 2 of 14: Context.sol
// SPDX-License-Identifier: MIT// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)pragmasolidity ^0.8.0;/**
* @dev Provides information about the current execution context, including the
* sender of the transaction and its data. While these are generally available
* via msg.sender and msg.data, they should not be accessed in such a direct
* manner, since when dealing with meta-transactions the account sending and
* paying for execution may not be the actual sender (as far as an application
* is concerned).
*
* This contract is only required for intermediate, library-like contracts.
*/abstractcontractContext{
function_msgSender() internalviewvirtualreturns (address) {
returnmsg.sender;
}
function_msgData() internalviewvirtualreturns (bytescalldata) {
returnmsg.data;
}
}
Contract Source Code
File 3 of 14: ERC165.sol
// SPDX-License-Identifier: MIT// OpenZeppelin Contracts v4.4.1 (utils/introspection/ERC165.sol)pragmasolidity ^0.8.0;import"./IERC165.sol";
/**
* @dev Implementation of the {IERC165} interface.
*
* Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check
* for the additional interface id that will be supported. For example:
*
* ```solidity
* function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
* return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
* }
* ```
*
* Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.
*/abstractcontractERC165isIERC165{
/**
* @dev See {IERC165-supportsInterface}.
*/functionsupportsInterface(bytes4 interfaceId) publicviewvirtualoverridereturns (bool) {
return interfaceId ==type(IERC165).interfaceId;
}
}
Contract Source Code
File 4 of 14: ERC721A.sol
// SPDX-License-Identifier: MIT// Creator: Chiru Labspragmasolidity ^0.8.4;import'@openzeppelin/contracts/token/ERC721/IERC721.sol';
import'@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol';
import'@openzeppelin/contracts/token/ERC721/extensions/IERC721Metadata.sol';
import'@openzeppelin/contracts/token/ERC721/extensions/IERC721Enumerable.sol';
import'@openzeppelin/contracts/utils/Address.sol';
import'@openzeppelin/contracts/utils/Context.sol';
import'@openzeppelin/contracts/utils/Strings.sol';
import'@openzeppelin/contracts/utils/introspection/ERC165.sol';
errorApprovalCallerNotOwnerNorApproved();
errorApprovalQueryForNonexistentToken();
errorApproveToCaller();
errorApprovalToCurrentOwner();
errorBalanceQueryForZeroAddress();
errorMintedQueryForZeroAddress();
errorBurnedQueryForZeroAddress();
errorMintToZeroAddress();
errorMintZeroQuantity();
errorOwnerIndexOutOfBounds();
errorOwnerQueryForNonexistentToken();
errorTokenIndexOutOfBounds();
errorTransferCallerNotOwnerNorApproved();
errorTransferFromIncorrectOwner();
errorTransferToNonERC721ReceiverImplementer();
errorTransferToZeroAddress();
errorURIQueryForNonexistentToken();
/**
* @dev Implementation of https://eips.ethereum.org/EIPS/eip-721[ERC721] Non-Fungible Token Standard, including
* the Metadata and Enumerable extension. Built to optimize for lower gas during batch mints.
*
* Assumes serials are sequentially minted starting at 0 (e.g. 0, 1, 2, 3..).
*
* Assumes that an owner cannot have more than 2**64 - 1 (max value of uint64) of supply.
*
* Assumes that the maximum token id cannot exceed 2**128 - 1 (max value of uint128).
*/contractERC721AisContext, ERC165, IERC721, IERC721Metadata, IERC721Enumerable{
usingAddressforaddress;
usingStringsforuint256;
// Compiler will pack this into a single 256bit word.structTokenOwnership {
// The address of the owner.address addr;
// Keeps track of the start time of ownership with minimal overhead for tokenomics.uint64 startTimestamp;
// Whether the token has been burned.bool burned;
}
// Compiler will pack this into a single 256bit word.structAddressData {
// Realistically, 2**64-1 is more than enough.uint64 balance;
// Keeps track of mint count with minimal overhead for tokenomics.uint64 numberMinted;
// Keeps track of burn count with minimal overhead for tokenomics.uint64 numberBurned;
}
// Compiler will pack the following // _currentIndex and _burnCounter into a single 256bit word.// The tokenId of the next token to be minted.uint128internal _currentIndex;
// The number of tokens burned.uint128internal _burnCounter;
// Token namestringprivate _name;
// Token symbolstringprivate _symbol;
// Mapping from token ID to ownership details// An empty struct value does not necessarily mean the token is unowned. See ownershipOf implementation for details.mapping(uint256=> TokenOwnership) internal _ownerships;
// Mapping owner address to address datamapping(address=> AddressData) private _addressData;
// Mapping from token ID to approved addressmapping(uint256=>address) private _tokenApprovals;
// Mapping from owner to operator approvalsmapping(address=>mapping(address=>bool)) private _operatorApprovals;
constructor(stringmemory name_, stringmemory symbol_) {
_name = name_;
_symbol = symbol_;
}
/**
* @dev See {IERC721Enumerable-totalSupply}.
*/functiontotalSupply() publicviewoverridereturns (uint256) {
// Counter underflow is impossible as _burnCounter cannot be incremented// more than _currentIndex timesunchecked {
return _currentIndex - _burnCounter;
}
}
/**
* @dev See {IERC721Enumerable-tokenByIndex}.
* This read function is O(totalSupply). If calling from a separate contract, be sure to test gas first.
* It may also degrade with extremely large collection sizes (e.g >> 10000), test for your use case.
*/functiontokenByIndex(uint256 index) publicviewoverridereturns (uint256) {
uint256 numMintedSoFar = _currentIndex;
uint256 tokenIdsIdx;
// Counter overflow is impossible as the loop breaks when// uint256 i is equal to another uint256 numMintedSoFar.unchecked {
for (uint256 i; i < numMintedSoFar; i++) {
TokenOwnership memory ownership = _ownerships[i];
if (!ownership.burned) {
if (tokenIdsIdx == index) {
return i;
}
tokenIdsIdx++;
}
}
}
revert TokenIndexOutOfBounds();
}
/**
* @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
* This read function is O(totalSupply). If calling from a separate contract, be sure to test gas first.
* It may also degrade with extremely large collection sizes (e.g >> 10000), test for your use case.
*/functiontokenOfOwnerByIndex(address owner, uint256 index) publicviewoverridereturns (uint256) {
if (index >= balanceOf(owner)) revert OwnerIndexOutOfBounds();
uint256 numMintedSoFar = _currentIndex;
uint256 tokenIdsIdx;
address currOwnershipAddr;
// Counter overflow is impossible as the loop breaks when// uint256 i is equal to another uint256 numMintedSoFar.unchecked {
for (uint256 i; i < numMintedSoFar; i++) {
TokenOwnership memory ownership = _ownerships[i];
if (ownership.burned) {
continue;
}
if (ownership.addr !=address(0)) {
currOwnershipAddr = ownership.addr;
}
if (currOwnershipAddr == owner) {
if (tokenIdsIdx == index) {
return i;
}
tokenIdsIdx++;
}
}
}
// Execution should never reach this point.revert();
}
/**
* @dev See {IERC165-supportsInterface}.
*/functionsupportsInterface(bytes4 interfaceId) publicviewvirtualoverride(ERC165, IERC165) returns (bool) {
return
interfaceId ==type(IERC721).interfaceId||
interfaceId ==type(IERC721Metadata).interfaceId||
interfaceId ==type(IERC721Enumerable).interfaceId||super.supportsInterface(interfaceId);
}
/**
* @dev See {IERC721-balanceOf}.
*/functionbalanceOf(address owner) publicviewoverridereturns (uint256) {
if (owner ==address(0)) revert BalanceQueryForZeroAddress();
returnuint256(_addressData[owner].balance);
}
function_numberMinted(address owner) internalviewreturns (uint256) {
if (owner ==address(0)) revert MintedQueryForZeroAddress();
returnuint256(_addressData[owner].numberMinted);
}
function_numberBurned(address owner) internalviewreturns (uint256) {
if (owner ==address(0)) revert BurnedQueryForZeroAddress();
returnuint256(_addressData[owner].numberBurned);
}
/**
* Gas spent here starts off proportional to the maximum mint batch size.
* It gradually moves to O(1) as tokens get transferred around in the collection over time.
*/functionownershipOf(uint256 tokenId) internalviewreturns (TokenOwnership memory) {
uint256 curr = tokenId;
unchecked {
if (curr < _currentIndex) {
TokenOwnership memory ownership = _ownerships[curr];
if (!ownership.burned) {
if (ownership.addr !=address(0)) {
return ownership;
}
// Invariant: // There will always be an ownership that has an address and is not burned // before an ownership that does not have an address and is not burned.// Hence, curr will not underflow.while (true) {
curr--;
ownership = _ownerships[curr];
if (ownership.addr !=address(0)) {
return ownership;
}
}
}
}
}
revert OwnerQueryForNonexistentToken();
}
/**
* @dev See {IERC721-ownerOf}.
*/functionownerOf(uint256 tokenId) publicviewoverridereturns (address) {
return ownershipOf(tokenId).addr;
}
/**
* @dev See {IERC721Metadata-name}.
*/functionname() publicviewvirtualoverridereturns (stringmemory) {
return _name;
}
/**
* @dev See {IERC721Metadata-symbol}.
*/functionsymbol() publicviewvirtualoverridereturns (stringmemory) {
return _symbol;
}
/**
* @dev See {IERC721Metadata-tokenURI}.
*/functiontokenURI(uint256 tokenId) publicviewvirtualoverridereturns (stringmemory) {
if (!_exists(tokenId)) revert URIQueryForNonexistentToken();
stringmemory baseURI = _baseURI();
returnbytes(baseURI).length!=0 ? string(abi.encodePacked(baseURI, tokenId.toString())) : '';
}
/**
* @dev Base URI for computing {tokenURI}. If set, the resulting URI for each
* token will be the concatenation of the `baseURI` and the `tokenId`. Empty
* by default, can be overriden in child contracts.
*/function_baseURI() internalviewvirtualreturns (stringmemory) {
return'';
}
/**
* @dev See {IERC721-approve}.
*/functionapprove(address to, uint256 tokenId) publicoverride{
address owner = ERC721A.ownerOf(tokenId);
if (to == owner) revert ApprovalToCurrentOwner();
if (_msgSender() != owner &&!isApprovedForAll(owner, _msgSender())) {
revert ApprovalCallerNotOwnerNorApproved();
}
_approve(to, tokenId, owner);
}
/**
* @dev See {IERC721-getApproved}.
*/functiongetApproved(uint256 tokenId) publicviewoverridereturns (address) {
if (!_exists(tokenId)) revert ApprovalQueryForNonexistentToken();
return _tokenApprovals[tokenId];
}
/**
* @dev See {IERC721-setApprovalForAll}.
*/functionsetApprovalForAll(address operator, bool approved) publicoverride{
if (operator == _msgSender()) revert ApproveToCaller();
_operatorApprovals[_msgSender()][operator] = approved;
emit ApprovalForAll(_msgSender(), operator, approved);
}
/**
* @dev See {IERC721-isApprovedForAll}.
*/functionisApprovedForAll(address owner, address operator) publicviewvirtualoverridereturns (bool) {
return _operatorApprovals[owner][operator];
}
/**
* @dev See {IERC721-transferFrom}.
*/functiontransferFrom(addressfrom,
address to,
uint256 tokenId
) publicvirtualoverride{
_transfer(from, to, tokenId);
}
/**
* @dev See {IERC721-safeTransferFrom}.
*/functionsafeTransferFrom(addressfrom,
address to,
uint256 tokenId
) publicvirtualoverride{
safeTransferFrom(from, to, tokenId, '');
}
/**
* @dev See {IERC721-safeTransferFrom}.
*/functionsafeTransferFrom(addressfrom,
address to,
uint256 tokenId,
bytesmemory _data
) publicvirtualoverride{
_transfer(from, to, tokenId);
if (!_checkOnERC721Received(from, to, tokenId, _data)) {
revert TransferToNonERC721ReceiverImplementer();
}
}
/**
* @dev Returns whether `tokenId` exists.
*
* Tokens can be managed by their owner or approved accounts via {approve} or {setApprovalForAll}.
*
* Tokens start existing when they are minted (`_mint`),
*/function_exists(uint256 tokenId) internalviewreturns (bool) {
return tokenId < _currentIndex &&!_ownerships[tokenId].burned;
}
function_safeMint(address to, uint256 quantity) internal{
_safeMint(to, quantity, '');
}
/**
* @dev Safely mints `quantity` tokens and transfers them to `to`.
*
* Requirements:
*
* - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called for each safe transfer.
* - `quantity` must be greater than 0.
*
* Emits a {Transfer} event.
*/function_safeMint(address to,
uint256 quantity,
bytesmemory _data
) internal{
_mint(to, quantity, _data, true);
}
/**
* @dev Mints `quantity` tokens and transfers them to `to`.
*
* Requirements:
*
* - `to` cannot be the zero address.
* - `quantity` must be greater than 0.
*
* Emits a {Transfer} event.
*/function_mint(address to,
uint256 quantity,
bytesmemory _data,
bool safe
) internal{
uint256 startTokenId = _currentIndex;
if (to ==address(0)) revert MintToZeroAddress();
if (quantity ==0) revert MintZeroQuantity();
_beforeTokenTransfers(address(0), to, startTokenId, quantity);
// Overflows are incredibly unrealistic.// balance or numberMinted overflow if current value of either + quantity > 3.4e38 (2**128) - 1// updatedIndex overflows if _currentIndex + quantity > 3.4e38 (2**128) - 1unchecked {
_addressData[to].balance+=uint64(quantity);
_addressData[to].numberMinted +=uint64(quantity);
_ownerships[startTokenId].addr = to;
_ownerships[startTokenId].startTimestamp =uint64(block.timestamp);
uint256 updatedIndex = startTokenId;
for (uint256 i; i < quantity; i++) {
emit Transfer(address(0), to, updatedIndex);
if (safe &&!_checkOnERC721Received(address(0), to, updatedIndex, _data)) {
revert TransferToNonERC721ReceiverImplementer();
}
updatedIndex++;
}
_currentIndex =uint128(updatedIndex);
}
_afterTokenTransfers(address(0), to, startTokenId, quantity);
}
/**
* @dev Transfers `tokenId` from `from` to `to`.
*
* Requirements:
*
* - `to` cannot be the zero address.
* - `tokenId` token must be owned by `from`.
*
* Emits a {Transfer} event.
*/function_transfer(addressfrom,
address to,
uint256 tokenId
) private{
TokenOwnership memory prevOwnership = ownershipOf(tokenId);
bool isApprovedOrOwner = (_msgSender() == prevOwnership.addr ||
isApprovedForAll(prevOwnership.addr, _msgSender()) ||
getApproved(tokenId) == _msgSender());
if (!isApprovedOrOwner) revert TransferCallerNotOwnerNorApproved();
if (prevOwnership.addr !=from) revert TransferFromIncorrectOwner();
if (to ==address(0)) revert TransferToZeroAddress();
_beforeTokenTransfers(from, to, tokenId, 1);
// Clear approvals from the previous owner
_approve(address(0), tokenId, prevOwnership.addr);
// 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**128.unchecked {
_addressData[from].balance-=1;
_addressData[to].balance+=1;
_ownerships[tokenId].addr = to;
_ownerships[tokenId].startTimestamp =uint64(block.timestamp);
// If the ownership slot of tokenId+1 is not explicitly set, that means the transfer initiator owns it.// Set the slot of tokenId+1 explicitly in storage to maintain correctness for ownerOf(tokenId+1) calls.uint256 nextTokenId = tokenId +1;
if (_ownerships[nextTokenId].addr ==address(0)) {
// This will suffice for checking _exists(nextTokenId),// as a burned slot cannot contain the zero address.if (nextTokenId < _currentIndex) {
_ownerships[nextTokenId].addr = prevOwnership.addr;
_ownerships[nextTokenId].startTimestamp = prevOwnership.startTimestamp;
}
}
}
emit Transfer(from, to, tokenId);
_afterTokenTransfers(from, to, tokenId, 1);
}
/**
* @dev Destroys `tokenId`.
* The approval is cleared when the token is burned.
*
* Requirements:
*
* - `tokenId` must exist.
*
* Emits a {Transfer} event.
*/function_burn(uint256 tokenId) internalvirtual{
TokenOwnership memory prevOwnership = ownershipOf(tokenId);
_beforeTokenTransfers(prevOwnership.addr, address(0), tokenId, 1);
// Clear approvals from the previous owner
_approve(address(0), tokenId, prevOwnership.addr);
// 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**128.unchecked {
_addressData[prevOwnership.addr].balance-=1;
_addressData[prevOwnership.addr].numberBurned +=1;
// Keep track of who burned the token, and the timestamp of burning.
_ownerships[tokenId].addr = prevOwnership.addr;
_ownerships[tokenId].startTimestamp =uint64(block.timestamp);
_ownerships[tokenId].burned =true;
// If the ownership slot of tokenId+1 is not explicitly set, that means the burn initiator owns it.// Set the slot of tokenId+1 explicitly in storage to maintain correctness for ownerOf(tokenId+1) calls.uint256 nextTokenId = tokenId +1;
if (_ownerships[nextTokenId].addr ==address(0)) {
// This will suffice for checking _exists(nextTokenId),// as a burned slot cannot contain the zero address.if (nextTokenId < _currentIndex) {
_ownerships[nextTokenId].addr = prevOwnership.addr;
_ownerships[nextTokenId].startTimestamp = prevOwnership.startTimestamp;
}
}
}
emit Transfer(prevOwnership.addr, address(0), tokenId);
_afterTokenTransfers(prevOwnership.addr, address(0), tokenId, 1);
// Overflow not possible, as _burnCounter cannot be exceed _currentIndex times.unchecked {
_burnCounter++;
}
}
/**
* @dev Approve `to` to operate on `tokenId`
*
* Emits a {Approval} event.
*/function_approve(address to,
uint256 tokenId,
address owner
) private{
_tokenApprovals[tokenId] = to;
emit Approval(owner, to, tokenId);
}
/**
* @dev Internal function to invoke {IERC721Receiver-onERC721Received} on a target address.
* The call is not executed if the target address is not a contract.
*
* @param from address representing the previous owner of the given token ID
* @param to target address that will receive the tokens
* @param tokenId uint256 ID of the token to be transferred
* @param _data bytes optional data to send along with the call
* @return bool whether the call correctly returned the expected magic value
*/function_checkOnERC721Received(addressfrom,
address to,
uint256 tokenId,
bytesmemory _data
) privatereturns (bool) {
if (to.isContract()) {
try IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, _data) returns (bytes4 retval) {
return retval == IERC721Receiver(to).onERC721Received.selector;
} catch (bytesmemory reason) {
if (reason.length==0) {
revert TransferToNonERC721ReceiverImplementer();
} else {
assembly {
revert(add(32, reason), mload(reason))
}
}
}
} else {
returntrue;
}
}
/**
* @dev Hook that is called before a set of serially-ordered token ids are about to be transferred. This includes minting.
* And also called before burning one token.
*
* startTokenId - the first token id to be transferred
* quantity - the amount to be transferred
*
* Calling conditions:
*
* - When `from` and `to` are both non-zero, `from`'s `tokenId` will be
* transferred to `to`.
* - When `from` is zero, `tokenId` will be minted for `to`.
* - When `to` is zero, `tokenId` will be burned by `from`.
* - `from` and `to` are never both zero.
*/function_beforeTokenTransfers(addressfrom,
address to,
uint256 startTokenId,
uint256 quantity
) internalvirtual{}
/**
* @dev Hook that is called after a set of serially-ordered token ids have been transferred. This includes
* minting.
* And also called after one token has been burned.
*
* startTokenId - the first token id to be transferred
* quantity - the amount to be transferred
*
* Calling conditions:
*
* - When `from` and `to` are both non-zero, `from`'s `tokenId` has been
* transferred to `to`.
* - When `from` is zero, `tokenId` has been minted for `to`.
* - When `to` is zero, `tokenId` has been burned by `from`.
* - `from` and `to` are never both zero.
*/function_afterTokenTransfers(addressfrom,
address to,
uint256 startTokenId,
uint256 quantity
) internalvirtual{}
}
Contract Source Code
File 5 of 14: IERC165.sol
// SPDX-License-Identifier: MIT// OpenZeppelin Contracts v4.4.1 (utils/introspection/IERC165.sol)pragmasolidity ^0.8.0;/**
* @dev Interface of the ERC165 standard, as defined in the
* https://eips.ethereum.org/EIPS/eip-165[EIP].
*
* Implementers can declare support of contract interfaces, which can then be
* queried by others ({ERC165Checker}).
*
* For an implementation, see {ERC165}.
*/interfaceIERC165{
/**
* @dev Returns true if this contract implements the interface defined by
* `interfaceId`. See the corresponding
* https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
* to learn more about how these ids are created.
*
* This function call must use less than 30 000 gas.
*/functionsupportsInterface(bytes4 interfaceId) externalviewreturns (bool);
}
Contract Source Code
File 6 of 14: IERC721.sol
// SPDX-License-Identifier: MIT// OpenZeppelin Contracts v4.4.1 (token/ERC721/IERC721.sol)pragmasolidity ^0.8.0;import"../../utils/introspection/IERC165.sol";
/**
* @dev Required interface of an ERC721 compliant contract.
*/interfaceIERC721isIERC165{
/**
* @dev Emitted when `tokenId` token is transferred from `from` to `to`.
*/eventTransfer(addressindexedfrom, addressindexed to, uint256indexed tokenId);
/**
* @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
*/eventApproval(addressindexed owner, addressindexed approved, uint256indexed tokenId);
/**
* @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
*/eventApprovalForAll(addressindexed owner, addressindexed operator, bool approved);
/**
* @dev Returns the number of tokens in ``owner``'s account.
*/functionbalanceOf(address owner) externalviewreturns (uint256 balance);
/**
* @dev Returns the owner of the `tokenId` token.
*
* Requirements:
*
* - `tokenId` must exist.
*/functionownerOf(uint256 tokenId) externalviewreturns (address owner);
/**
* @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
* are aware of the ERC721 protocol to prevent tokens from being forever locked.
*
* Requirements:
*
* - `from` cannot be the zero address.
* - `to` cannot be the zero address.
* - `tokenId` token must exist and be owned by `from`.
* - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
* - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
*
* Emits a {Transfer} event.
*/functionsafeTransferFrom(addressfrom,
address to,
uint256 tokenId
) external;
/**
* @dev Transfers `tokenId` token from `from` to `to`.
*
* WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
*
* Requirements:
*
* - `from` cannot be the zero address.
* - `to` cannot be the zero address.
* - `tokenId` token must be owned by `from`.
* - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
*
* Emits a {Transfer} event.
*/functiontransferFrom(addressfrom,
address to,
uint256 tokenId
) external;
/**
* @dev Gives permission to `to` to transfer `tokenId` token to another account.
* The approval is cleared when the token is transferred.
*
* Only a single account can be approved at a time, so approving the zero address clears previous approvals.
*
* Requirements:
*
* - The caller must own the token or be an approved operator.
* - `tokenId` must exist.
*
* Emits an {Approval} event.
*/functionapprove(address to, uint256 tokenId) external;
/**
* @dev Returns the account approved for `tokenId` token.
*
* Requirements:
*
* - `tokenId` must exist.
*/functiongetApproved(uint256 tokenId) externalviewreturns (address operator);
/**
* @dev Approve or remove `operator` as an operator for the caller.
* Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
*
* Requirements:
*
* - The `operator` cannot be the caller.
*
* Emits an {ApprovalForAll} event.
*/functionsetApprovalForAll(address operator, bool _approved) external;
/**
* @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
*
* See {setApprovalForAll}
*/functionisApprovedForAll(address owner, address operator) externalviewreturns (bool);
/**
* @dev Safely transfers `tokenId` token from `from` to `to`.
*
* Requirements:
*
* - `from` cannot be the zero address.
* - `to` cannot be the zero address.
* - `tokenId` token must exist and be owned by `from`.
* - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
* - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
*
* Emits a {Transfer} event.
*/functionsafeTransferFrom(addressfrom,
address to,
uint256 tokenId,
bytescalldata data
) external;
}
Contract Source Code
File 7 of 14: IERC721Enumerable.sol
// SPDX-License-Identifier: MIT// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC721/extensions/IERC721Enumerable.sol)pragmasolidity ^0.8.0;import"../IERC721.sol";
/**
* @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
* @dev See https://eips.ethereum.org/EIPS/eip-721
*/interfaceIERC721EnumerableisIERC721{
/**
* @dev Returns the total amount of tokens stored by the contract.
*/functiontotalSupply() externalviewreturns (uint256);
/**
* @dev Returns a token ID owned by `owner` at a given `index` of its token list.
* Use along with {balanceOf} to enumerate all of ``owner``'s tokens.
*/functiontokenOfOwnerByIndex(address owner, uint256 index) externalviewreturns (uint256);
/**
* @dev Returns a token ID at a given `index` of all the tokens stored by the contract.
* Use along with {totalSupply} to enumerate all tokens.
*/functiontokenByIndex(uint256 index) externalviewreturns (uint256);
}
// SPDX-License-Identifier: MIT// OpenZeppelin Contracts v4.4.1 (token/ERC721/IERC721Receiver.sol)pragmasolidity ^0.8.0;/**
* @title ERC721 token receiver interface
* @dev Interface for any contract that wants to support safeTransfers
* from ERC721 asset contracts.
*/interfaceIERC721Receiver{
/**
* @dev Whenever an {IERC721} `tokenId` token is transferred to this contract via {IERC721-safeTransferFrom}
* by `operator` from `from`, this function is called.
*
* It must return its Solidity selector to confirm the token transfer.
* If any other value is returned or the interface is not implemented by the recipient, the transfer will be reverted.
*
* The selector can be obtained in Solidity with `IERC721.onERC721Received.selector`.
*/functiononERC721Received(address operator,
addressfrom,
uint256 tokenId,
bytescalldata data
) externalreturns (bytes4);
}
Contract Source Code
File 10 of 14: Kiwami.sol
//SPDX-License-Identifier: MITpragmasolidity ^0.8.4;import"@openzeppelin/contracts/access/Ownable.sol";
import"erc721a/contracts/ERC721A.sol";
import"./MerkleWhitelist.sol";
import"@openzeppelin/contracts/utils/Strings.sol";
/*
Kiwami.sol
Written by: mousedev.eth
Dutch Auction style inspired by: 0xinuarashi
*/contractKiwamiisOwnable, ERC721A, MerkleWhitelist{
//Starting at 0.5 etheruint256public DA_STARTING_PRICE =0.5ether;
//Ending at 0.1 etheruint256public DA_ENDING_PRICE =0.1ether;
//Decrease by 0.05 every frequency.uint256public DA_DECREMENT =0.05ether;
//decrement price every 180 seconds (3 minutes).uint256public DA_DECREMENT_FREQUENCY =180;
//Starting DA time (seconds).uint256public DA_STARTING_TIMESTAMP =1648080000;
//The final auction price.uint256public DA_FINAL_PRICE;
//The quantity for DA.uint256public DA_QUANTITY =7000;
//How many publicWL have been minteduint16public PUBLIC_WL_MINTED;
boolpublic INITIAL_FUNDS_WITHDRAWN;
boolpublic REMAINING_FUNDS_WITHDRAWN;
addresspublic TEAM_USA_ADDRESS =0x0E861ddDA17f7C20996dC0868cAcc200bc1985c0;
addresspublic TEAM_JAPAN_ADDRESS =0xBC77EDd603bEf4004c47A831fDDa437cD906442E;
addresspublic MULTISIG_ADDRESS =0xBcAf5e757Ca1ef5F35fC2daBaDcb71dC7418A40D;
//Contract URIstringpublic CONTRACT_URI ="ipfs://QmNx5M7Dvgvg6ZNmUX6pdfD4NWZ7oh6RiP2F5b33TrPxCJ";
//Struct for storing batch price data.structTokenBatchPriceData {
uint128 pricePaid;
uint8 quantityMinted;
}
//Token to token price datamapping(address=> TokenBatchPriceData[]) public userToTokenBatchPriceData;
mapping(address=>bool) public userToHasMintedPublicWL;
mapping(address=>bool) public userToHasMintedMiceWL;
boolpublic REVEALED;
stringpublic UNREVEALED_URI ="ipfs://QmWQMuChCoTc2jKoDqCVHBxYe6pp1E2KMyW4HG8U7AA6wF";
stringpublic BASE_URI;
uint256public publicWLStartTime =1648166400;
uint256public miceWLStartTime =1648598400;
constructor() ERC721A("Kiwami", "KIWAMI") {}
functioncurrentPrice() publicviewreturns (uint256) {
require(
block.timestamp>= DA_STARTING_TIMESTAMP,
"DA has not started!"
);
if (DA_FINAL_PRICE >0) return DA_FINAL_PRICE;
//Seconds since we starteduint256 timeSinceStart =block.timestamp- DA_STARTING_TIMESTAMP;
//How many decrements should've happened since that timeuint256 decrementsSinceStart = timeSinceStart / DA_DECREMENT_FREQUENCY;
//How much eth to removeuint256 totalDecrement = decrementsSinceStart * DA_DECREMENT;
//If how much we want to reduce is greater or equal to the range, return the lowest valueif (totalDecrement >= DA_STARTING_PRICE - DA_ENDING_PRICE) {
return DA_ENDING_PRICE;
}
//If not, return the starting price minus the decrement.return DA_STARTING_PRICE - totalDecrement;
}
functionmintDutchAuction(uint8 quantity) publicpayable{
//Require DA startedrequire(
block.timestamp>= DA_STARTING_TIMESTAMP,
"DA has not started!"
);
//Require max 5require(quantity >0&& quantity <6, "Can only mint max 5 NFTs!");
uint256 _currentPrice = currentPrice();
//Require enough ETHrequire(
msg.value>= quantity * _currentPrice,
"Did not send enough eth."
);
//Max supplyrequire(
totalSupply() + quantity <= DA_QUANTITY,
"Max supply for DA reached!"
);
//This is the final priceif (totalSupply() + quantity == DA_QUANTITY)
DA_FINAL_PRICE = _currentPrice;
userToTokenBatchPriceData[msg.sender].push(
TokenBatchPriceData(uint128(msg.value), quantity)
);
//Mint the quantity
_safeMint(msg.sender, quantity);
}
functionmintPublicWL(bytes32[] memory proof)
publicpayableonlyPublicWhitelist(proof)
{
require(DA_FINAL_PRICE >0, "Dutch action must be over!");
require(
!userToHasMintedPublicWL[msg.sender],
"Can only mint once during public WL!"
);
require(
block.timestamp>= publicWLStartTime,
"Public WL has not started yet!"
);
require(
msg.value>= ((DA_FINAL_PRICE /100) *80),
"Must send enough eth for WL Mint"
);
//Require max supply just in case.require(totalSupply() +1<=8500, "Max supply of 8,500!");
userToHasMintedPublicWL[msg.sender] =true;
PUBLIC_WL_MINTED++;
//Mint them
_safeMint(msg.sender, 1);
}
functionmintMouseWL(bytes32[] memory proof)
publiconlyMouseWhitelist(proof)
{
require(DA_FINAL_PRICE >0, "Dutch action must be over!");
require(
!userToHasMintedMiceWL[msg.sender],
"Can only mint once during mouse WL!"
);
require(
block.timestamp>= miceWLStartTime,
"Mice WL has not started yet!"
);
//Require max supply just in case.require(totalSupply() +1<=10000, "Max supply of 10,000!");
userToHasMintedMiceWL[msg.sender] =true;
//Mint them
_safeMint(msg.sender, 1);
}
functionteamMint(uint256 quantity, address receiver) publiconlyOwner{
//Max supplyrequire(
totalSupply() + quantity <=10000,
"Max supply of 10,000 total!"
);
require(DA_FINAL_PRICE >0, "Dutch action must be over!");
//Mint the quantity
_safeMint(receiver, quantity);
}
functionuserToTokenBatchLength(address user)
publicviewreturns (uint256)
{
return userToTokenBatchPriceData[user].length;
}
functionrefundExtraETH() public{
require(DA_FINAL_PRICE >0, "Dutch action must be over!");
uint256 totalRefund;
for (
uint256 i = userToTokenBatchPriceData[msg.sender].length;
i >0;
i--
) {
//This is what they should have paid if they bought at lowest price tier.uint256 expectedPrice = userToTokenBatchPriceData[msg.sender][i -1]
.quantityMinted * DA_FINAL_PRICE;
//What they paid - what they should have paid = refund.uint256 refund = userToTokenBatchPriceData[msg.sender][i -1]
.pricePaid - expectedPrice;
//Remove this tokenBatch
userToTokenBatchPriceData[msg.sender].pop();
//Send them their extra monies.
totalRefund += refund;
}
payable(msg.sender).transfer(totalRefund);
}
functionwithdrawInitialFunds() publiconlyOwner{
require(
!INITIAL_FUNDS_WITHDRAWN,
"Initial funds have already been withdrawn."
);
require(DA_FINAL_PRICE >0, "DA has not finished!");
uint256 DAFunds = DA_QUANTITY * DA_FINAL_PRICE;
uint256 publicWLFunds = PUBLIC_WL_MINTED *
((DA_FINAL_PRICE /100) *80);
uint256 initialFunds = DAFunds + publicWLFunds;
INITIAL_FUNDS_WITHDRAWN =true;
(bool succ, ) =payable(TEAM_USA_ADDRESS).call{
value: (initialFunds *15) /100
}("");
require(succ, "transfer failed");
(succ, ) =payable(TEAM_JAPAN_ADDRESS).call{
value: (initialFunds *35) /100
}("");
require(succ, "transfer failed");
(succ, ) =payable(MULTISIG_ADDRESS).call{
value: (initialFunds *50) /100
}("");
require(succ, "transfer failed");
}
functionwithdrawFinalFunds() publiconlyOwner{
//Require this is 1 weeks after DA Start.require(block.timestamp>= DA_STARTING_TIMESTAMP +604800);
uint256 finalFunds =address(this).balance;
(bool succ, ) =payable(TEAM_USA_ADDRESS).call{
value: (finalFunds *15) /100
}("");
require(succ, "transfer failed");
(succ, ) =payable(TEAM_JAPAN_ADDRESS).call{
value: (finalFunds *35) /100
}("");
require(succ, "transfer failed");
(succ, ) =payable(MULTISIG_ADDRESS).call{
value: (finalFunds *50) /100
}("");
require(succ, "transfer failed");
}
functionsetRevealData(bool _revealed, stringmemory _unrevealedURI)
publiconlyOwner{
REVEALED = _revealed;
UNREVEALED_URI = _unrevealedURI;
}
functionsetBaseURI(stringmemory _baseURI) publiconlyOwner{
BASE_URI = _baseURI;
}
functioncontractURI() publicviewreturns (stringmemory) {
return CONTRACT_URI;
}
functionsetContractURI(stringmemory _contractURI) publiconlyOwner{
CONTRACT_URI = _contractURI;
}
functiontokenURI(uint256 _tokenId)
publicviewoverridereturns (stringmemory)
{
if (REVEALED) {
returnstring(abi.encodePacked(BASE_URI, Strings.toString(_tokenId)));
} else {
return UNREVEALED_URI;
}
}
}
Contract Source Code
File 11 of 14: MerkleProof.sol
// SPDX-License-Identifier: MIT// OpenZeppelin Contracts (last updated v4.5.0) (utils/cryptography/MerkleProof.sol)pragmasolidity ^0.8.0;/**
* @dev These functions deal with verification of Merkle Trees proofs.
*
* The proofs can be generated using the JavaScript library
* https://github.com/miguelmota/merkletreejs[merkletreejs].
* Note: the hashing algorithm should be keccak256 and pair sorting should be enabled.
*
* See `test/utils/cryptography/MerkleProof.test.js` for some examples.
*/libraryMerkleProof{
/**
* @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
* defined by `root`. For this, a `proof` must be provided, containing
* sibling hashes on the branch from the leaf to the root of the tree. Each
* pair of leaves and each pair of pre-images are assumed to be sorted.
*/functionverify(bytes32[] memory proof,
bytes32 root,
bytes32 leaf
) internalpurereturns (bool) {
return processProof(proof, leaf) == root;
}
/**
* @dev Returns the rebuilt hash obtained by traversing a Merklee tree up
* from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
* hash matches the root of the tree. When processing the proof, the pairs
* of leafs & pre-images are assumed to be sorted.
*
* _Available since v4.4._
*/functionprocessProof(bytes32[] memory proof, bytes32 leaf) internalpurereturns (bytes32) {
bytes32 computedHash = leaf;
for (uint256 i =0; i < proof.length; i++) {
bytes32 proofElement = proof[i];
if (computedHash <= proofElement) {
// Hash(current computed hash + current element of the proof)
computedHash = _efficientHash(computedHash, proofElement);
} else {
// Hash(current element of the proof + current computed hash)
computedHash = _efficientHash(proofElement, computedHash);
}
}
return computedHash;
}
function_efficientHash(bytes32 a, bytes32 b) privatepurereturns (bytes32 value) {
assembly {
mstore(0x00, a)
mstore(0x20, b)
value :=keccak256(0x00, 0x40)
}
}
}
// SPDX-License-Identifier: MIT// OpenZeppelin Contracts v4.4.1 (access/Ownable.sol)pragmasolidity ^0.8.0;import"../utils/Context.sol";
/**
* @dev Contract module which provides a basic access control mechanism, where
* there is an account (an owner) that can be granted exclusive access to
* specific functions.
*
* By default, the owner account will be the one that deploys the contract. This
* can later be changed with {transferOwnership}.
*
* This module is used through inheritance. It will make available the modifier
* `onlyOwner`, which can be applied to your functions to restrict their use to
* the owner.
*/abstractcontractOwnableisContext{
addressprivate _owner;
eventOwnershipTransferred(addressindexed previousOwner, addressindexed newOwner);
/**
* @dev Initializes the contract setting the deployer as the initial owner.
*/constructor() {
_transferOwnership(_msgSender());
}
/**
* @dev Returns the address of the current owner.
*/functionowner() publicviewvirtualreturns (address) {
return _owner;
}
/**
* @dev Throws if called by any account other than the owner.
*/modifieronlyOwner() {
require(owner() == _msgSender(), "Ownable: caller is not the owner");
_;
}
/**
* @dev Leaves the contract without owner. It will not be possible to call
* `onlyOwner` functions anymore. Can only be called by the current owner.
*
* NOTE: Renouncing ownership will leave the contract without an owner,
* thereby removing any functionality that is only available to the owner.
*/functionrenounceOwnership() publicvirtualonlyOwner{
_transferOwnership(address(0));
}
/**
* @dev Transfers ownership of the contract to a new account (`newOwner`).
* Can only be called by the current owner.
*/functiontransferOwnership(address newOwner) publicvirtualonlyOwner{
require(newOwner !=address(0), "Ownable: new owner is the zero address");
_transferOwnership(newOwner);
}
/**
* @dev Transfers ownership of the contract to a new account (`newOwner`).
* Internal function without access restriction.
*/function_transferOwnership(address newOwner) internalvirtual{
address oldOwner = _owner;
_owner = newOwner;
emit OwnershipTransferred(oldOwner, newOwner);
}
}
Contract Source Code
File 14 of 14: Strings.sol
// SPDX-License-Identifier: MIT// OpenZeppelin Contracts v4.4.1 (utils/Strings.sol)pragmasolidity ^0.8.0;/**
* @dev String operations.
*/libraryStrings{
bytes16privateconstant _HEX_SYMBOLS ="0123456789abcdef";
/**
* @dev Converts a `uint256` to its ASCII `string` decimal representation.
*/functiontoString(uint256 value) internalpurereturns (stringmemory) {
// Inspired by OraclizeAPI's implementation - MIT licence// https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.solif (value ==0) {
return"0";
}
uint256 temp = value;
uint256 digits;
while (temp !=0) {
digits++;
temp /=10;
}
bytesmemory buffer =newbytes(digits);
while (value !=0) {
digits -=1;
buffer[digits] =bytes1(uint8(48+uint256(value %10)));
value /=10;
}
returnstring(buffer);
}
/**
* @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
*/functiontoHexString(uint256 value) internalpurereturns (stringmemory) {
if (value ==0) {
return"0x00";
}
uint256 temp = value;
uint256 length =0;
while (temp !=0) {
length++;
temp >>=8;
}
return toHexString(value, length);
}
/**
* @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
*/functiontoHexString(uint256 value, uint256 length) internalpurereturns (stringmemory) {
bytesmemory buffer =newbytes(2* length +2);
buffer[0] ="0";
buffer[1] ="x";
for (uint256 i =2* length +1; i >1; --i) {
buffer[i] = _HEX_SYMBOLS[value &0xf];
value >>=4;
}
require(value ==0, "Strings: hex length insufficient");
returnstring(buffer);
}
}