Contract Source Code:
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
/**
* @dev Interface of the ERC20 standard as defined in the EIP.
*/
interface IERC20 {
/**
* @dev Returns the amount of tokens in existence.
*/
function totalSupply() external view returns (uint256);
/**
* @dev Returns the amount of tokens owned by `account`.
*/
function balanceOf(address account) external view returns (uint256);
/**
* @dev Moves `amount` tokens from the caller's account to `recipient`.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a {Transfer} event.
*/
function transfer(address recipient, uint256 amount) external returns (bool);
/**
* @dev Returns the remaining number of tokens that `spender` will be
* allowed to spend on behalf of `owner` through {transferFrom}. This is
* zero by default.
*
* This value changes when {approve} or {transferFrom} are called.
*/
function allowance(address owner, address spender) external view returns (uint256);
/**
* @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* IMPORTANT: Beware that changing an allowance with this method brings the risk
* that someone may use both the old and the new allowance by unfortunate
* transaction ordering. One possible solution to mitigate this race
* condition is to first reduce the spender's allowance to 0 and set the
* desired value afterwards:
* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
*
* Emits an {Approval} event.
*/
function approve(address spender, uint256 amount) external returns (bool);
/**
* @dev Moves `amount` tokens from `sender` to `recipient` using the
* allowance mechanism. `amount` is then deducted from the caller's
* allowance.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a {Transfer} event.
*/
function transferFrom(
address sender,
address recipient,
uint256 amount
) external returns (bool);
/**
* @dev Emitted when `value` tokens are moved from one account (`from`) to
* another (`to`).
*
* Note that `value` may be zero.
*/
event Transfer(address indexed from, address indexed to, uint256 value);
/**
* @dev Emitted when the allowance of a `spender` for an `owner` is set by
* a call to {approve}. `value` is the new allowance.
*/
event Approval(address indexed owner, address indexed spender, uint256 value);
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "../IERC20.sol";
import "../../../utils/Address.sol";
/**
* @title SafeERC20
* @dev Wrappers around ERC20 operations that throw on failure (when the token
* contract returns false). Tokens that return no value (and instead revert or
* throw on failure) are also supported, non-reverting calls are assumed to be
* successful.
* To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
* which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
*/
library SafeERC20 {
using Address for address;
function safeTransfer(
IERC20 token,
address to,
uint256 value
) internal {
_callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
}
function safeTransferFrom(
IERC20 token,
address from,
address to,
uint256 value
) internal {
_callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
}
/**
* @dev Deprecated. This function has issues similar to the ones found in
* {IERC20-approve}, and its usage is discouraged.
*
* Whenever possible, use {safeIncreaseAllowance} and
* {safeDecreaseAllowance} instead.
*/
function safeApprove(
IERC20 token,
address spender,
uint256 value
) internal {
// safeApprove should only be called when setting an initial allowance,
// or when resetting it to zero. To increase and decrease it, use
// 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
require(
(value == 0) || (token.allowance(address(this), spender) == 0),
"SafeERC20: approve from non-zero to non-zero allowance"
);
_callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
}
function safeIncreaseAllowance(
IERC20 token,
address spender,
uint256 value
) internal {
uint256 newAllowance = token.allowance(address(this), spender) + value;
_callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
}
function safeDecreaseAllowance(
IERC20 token,
address spender,
uint256 value
) internal {
unchecked {
uint256 oldAllowance = token.allowance(address(this), spender);
require(oldAllowance >= value, "SafeERC20: decreased allowance below zero");
uint256 newAllowance = oldAllowance - value;
_callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
}
}
/**
* @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
* on the return value: the return value is optional (but if data is returned, it must not be false).
* @param token The token targeted by the call.
* @param data The call data (encoded using abi.encode or one of its variants).
*/
function _callOptionalReturn(IERC20 token, bytes memory data) private {
// We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
// we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
// the target address contains contract code and also asserts for success in the low-level call.
bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
if (returndata.length > 0) {
// Return data is optional
require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
}
}
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
/**
* @dev Collection of functions related to the address type
*/
library Address {
/**
* @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
* ====
*/
function isContract(address account) internal view returns (bool) {
// This method relies on extcodesize, which returns 0 for contracts in
// construction, since the code is only stored at the end of the
// constructor execution.
uint256 size;
assembly {
size := extcodesize(account)
}
return size > 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].
*/
function sendValue(address payable 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._
*/
function functionCall(address target, bytes memory data) internal returns (bytes memory) {
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._
*/
function functionCall(
address target,
bytes memory data,
string memory errorMessage
) internal returns (bytes memory) {
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._
*/
function functionCallWithValue(
address target,
bytes memory data,
uint256 value
) internal returns (bytes memory) {
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._
*/
function functionCallWithValue(
address target,
bytes memory data,
uint256 value,
string memory errorMessage
) internal returns (bytes memory) {
require(address(this).balance >= value, "Address: insufficient balance for call");
require(isContract(target), "Address: call to non-contract");
(bool success, bytes memory 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._
*/
function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
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._
*/
function functionStaticCall(
address target,
bytes memory data,
string memory errorMessage
) internal view returns (bytes memory) {
require(isContract(target), "Address: static call to non-contract");
(bool success, bytes memory 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._
*/
function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
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._
*/
function functionDelegateCall(
address target,
bytes memory data,
string memory errorMessage
) internal returns (bytes memory) {
require(isContract(target), "Address: delegate call to non-contract");
(bool success, bytes memory 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._
*/
function verifyCallResult(
bool success,
bytes memory returndata,
string memory errorMessage
) internal pure returns (bytes memory) {
if (success) {
return returndata;
} else {
// Look for revert reason and bubble it up if present
if (returndata.length > 0) {
// The easiest way to bubble the revert reason is using memory via assembly
assembly {
let returndata_size := mload(returndata)
revert(add(32, returndata), returndata_size)
}
} else {
revert(errorMessage);
}
}
}
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
contract Config {
// function signature of "postProcess()"
bytes4 public constant POSTPROCESS_SIG = 0xc2722916;
// The base amount of percentage function
uint256 public constant PERCENTAGE_BASE = 1 ether;
// Handler post-process type. Others should not happen now.
enum HandlerType {
Token,
Custom,
Others
}
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "./lib/LibCache.sol";
import "./lib/LibStack.sol";
/// @notice A cache structure composed by a bytes32 array
contract Storage {
using LibCache for mapping(bytes32 => bytes32);
using LibStack for bytes32[];
bytes32[] public stack;
mapping(bytes32 => bytes32) public cache;
// keccak256 hash of "msg.sender"
// prettier-ignore
bytes32 public constant MSG_SENDER_KEY = 0xb2f2618cecbbb6e7468cc0f2aa43858ad8d153e0280b22285e28e853bb9d453a;
modifier isStackEmpty() {
require(stack.length == 0, "Stack not empty");
_;
}
modifier isInitialized() {
require(_getSender() != address(0), "Sender is not initialized");
_;
}
modifier isNotInitialized() {
require(_getSender() == address(0), "Sender is initialized");
_;
}
function _setSender() internal isNotInitialized {
cache.setAddress(MSG_SENDER_KEY, msg.sender);
}
function _resetSender() internal {
cache.setAddress(MSG_SENDER_KEY, address(0));
}
function _getSender() internal view returns (address) {
return cache.getAddress(MSG_SENDER_KEY);
}
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "../interface/IERC20Usdt.sol";
import "../Config.sol";
import "../Storage.sol";
abstract contract HandlerBase is Storage, Config {
using SafeERC20 for IERC20;
using LibStack for bytes32[];
address public constant NATIVE_TOKEN_ADDRESS =
0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
function postProcess() external payable virtual {
revert("Invalid post process");
/* Implementation template
bytes4 sig = stack.getSig();
if (sig == bytes4(keccak256(bytes("handlerFunction_1()")))) {
// Do something
} else if (sig == bytes4(keccak256(bytes("handlerFunction_2()")))) {
bytes32 temp = stack.get();
// Do something
} else revert("Invalid post process");
*/
}
function _updateToken(address token) internal {
stack.setAddress(token);
// Ignore token type to fit old handlers
// stack.setHandlerType(uint256(HandlerType.Token));
}
function _updatePostProcess(bytes32[] memory params) internal {
for (uint256 i = params.length; i > 0; i--) {
stack.set(params[i - 1]);
}
stack.set(msg.sig);
stack.setHandlerType(HandlerType.Custom);
}
function getContractName() public pure virtual returns (string memory);
function _revertMsg(
string memory functionName,
string memory reason
) internal pure {
revert(
string(
abi.encodePacked(
getContractName(),
"_",
functionName,
": ",
reason
)
)
);
}
function _revertMsg(string memory functionName) internal pure {
_revertMsg(functionName, "Unspecified");
}
function _requireMsg(
bool condition,
string memory functionName,
string memory reason
) internal pure {
if (!condition) _revertMsg(functionName, reason);
}
function _uint2String(uint256 n) internal pure returns (string memory) {
if (n == 0) {
return "0";
} else {
uint256 len = 0;
for (uint256 temp = n; temp > 0; temp /= 10) {
len++;
}
bytes memory str = new bytes(len);
for (uint256 i = len; i > 0; i--) {
str[i - 1] = bytes1(uint8(48 + (n % 10)));
n /= 10;
}
return string(str);
}
}
function _getBalance(
address token,
uint256 amount
) internal view returns (uint256) {
if (amount != type(uint256).max) {
return amount;
}
// ETH case
if (token == address(0) || token == NATIVE_TOKEN_ADDRESS) {
return address(this).balance;
}
// ERC20 token case
return IERC20(token).balanceOf(address(this));
}
function _tokenApprove(
address token,
address spender,
uint256 amount
) internal {
try IERC20Usdt(token).approve(spender, amount) {} catch {
IERC20(token).safeApprove(spender, 0);
IERC20(token).safeApprove(spender, amount);
}
}
function _tokenApproveZero(address token, address spender) internal {
if (IERC20Usdt(token).allowance(address(this), spender) > 0) {
try IERC20Usdt(token).approve(spender, 0) {} catch {
IERC20Usdt(token).approve(spender, 1);
}
}
}
function _isNotNativeToken(address token) internal pure returns (bool) {
return (token != address(0) && token != NATIVE_TOKEN_ADDRESS);
}
}
// SPDX-License-Identifier: MIT
pragma solidity 0.8.10;
import {HandlerBase} from "../HandlerBase.sol";
import {IStargateRouter, IStargateWidget} from "./IStargateRouter.sol";
import {IStargateRouterETH} from "./IStargateRouterETH.sol";
import {IStargateToken} from "./IStargateToken.sol";
import {IFactory, IPool} from "./IFactory.sol";
contract HStargate is HandlerBase {
address public immutable router;
address public immutable routerETH;
address public immutable stgToken;
address public immutable factory;
address public immutable widgetSwap;
bytes2 public immutable partnerId;
constructor(
address router_,
address routerETH_,
address stgToken_,
address factory_,
address widgetSwap_,
bytes2 partnerId_
) {
router = router_;
routerETH = routerETH_;
stgToken = stgToken_;
factory = factory_;
widgetSwap = widgetSwap_;
partnerId = partnerId_;
}
function getContractName() public pure override returns (string memory) {
return "HStargate";
}
function swapETH(
uint16 dstChainId,
address payable refundAddress,
uint256 amountIn,
uint256 fee,
uint256 amountOutMin,
address to
) external payable {
_requireMsg(to != address(0), "swapETH", "to zero address");
uint256 value;
if (amountIn != type(uint256).max) {
value = amountIn + fee;
} else {
value = address(this).balance;
amountIn = value - fee;
}
// Swap ETH
try
IStargateRouterETH(routerETH).swapETH{value: value}(
dstChainId,
refundAddress,
abi.encodePacked(to),
amountIn,
amountOutMin
)
{} catch Error(string memory reason) {
_revertMsg("swapETH", reason);
} catch {
_revertMsg("swapETH");
}
// Partnership
IStargateWidget(widgetSwap).partnerSwap(partnerId);
}
function swap(
uint16 dstChainId,
uint256 srcPoolId,
uint256 dstPoolId,
address payable refundAddress,
uint256 amountIn,
uint256 fee,
uint256 amountOutMin,
address to
) external payable {
_requireMsg(to != address(0), "swap", "to zero address");
// Approve input token to Stargate
IPool pool = IFactory(factory).getPool(srcPoolId);
_requireMsg(address(pool) != address(0), "swap", "pool not found");
address tokenIn = pool.token();
amountIn = _getBalance(tokenIn, amountIn);
_tokenApprove(tokenIn, router, amountIn);
// Swap input token
try
IStargateRouter(router).swap{value: fee}(
dstChainId,
srcPoolId,
dstPoolId,
refundAddress,
amountIn,
amountOutMin,
IStargateRouter.lzTxObj(0, 0, "0x"), // no destination gas
abi.encodePacked(to),
bytes("") // no data
)
{} catch Error(string memory reason) {
_revertMsg("swap", reason);
} catch {
_revertMsg("swap");
}
// Reset Approval
_tokenApproveZero(tokenIn, router);
// Partnership
IStargateWidget(widgetSwap).partnerSwap(partnerId);
}
function sendTokens(
uint16 dstChainId,
address to,
uint256 amountIn,
uint256 fee,
uint256 dstGas
) external payable {
_requireMsg(to != address(0), "sendTokens", "to zero address");
_requireMsg(amountIn != 0, "sendTokens", "zero amountIn");
amountIn = _getBalance(stgToken, amountIn);
// Send STG token
try
IStargateToken(stgToken).sendTokens{value: fee}(
dstChainId,
abi.encodePacked(to),
amountIn,
address(0),
abi.encodePacked(uint16(1) /* version */, dstGas)
)
{} catch Error(string memory reason) {
_revertMsg("sendTokens", reason);
} catch {
_revertMsg("sendTokens");
}
// Partnership
IStargateWidget(widgetSwap).partnerSwap(partnerId);
}
}
// SPDX-License-Identifier: BUSL-1.1
pragma solidity ^0.8.0;
import "./IPool.sol";
interface IFactory {
function getPool(uint256 poolId) external view returns(IPool);
}
// SPDX-License-Identifier: BUSL-1.1
pragma solidity ^0.8.0;
interface IPool {
function token() external view returns(address);
}
// SPDX-License-Identifier: BUSL-1.1
pragma solidity ^0.8.0;
interface IStargateWidget {
function partnerSwap(bytes2 _partnerId) external;
event PartnerSwap(bytes2 indexed partnerId);
}
interface IStargateRouter {
struct lzTxObj {
uint256 dstGasForCall;
uint256 dstNativeAmount;
bytes dstNativeAddr;
}
function swap(
uint16 _dstChainId,
uint256 _srcPoolId,
uint256 _dstPoolId,
address payable _refundAddress,
uint256 _amountLD,
uint256 _minAmountLD,
lzTxObj memory _lzTxParams,
bytes calldata _to,
bytes calldata _payload
) external payable;
function quoteLayerZeroFee(
uint16 _dstChainId,
uint8 _functionType,
bytes calldata _toAddress,
bytes calldata _transferAndCallPayload,
lzTxObj memory _lzTxParams
) external view returns (uint256 /*nativeFee*/, uint256 /*layerZeroFee*/);
}
// SPDX-License-Identifier: BUSL-1.1
pragma solidity ^0.8.0;
interface IStargateRouterETH {
function swapETH(
uint16 _dstChainId, // destination Stargate chainId
address payable _refundAddress, // refund additional messageFee to this address
bytes calldata _toAddress, // the receiver of the destination ETH
uint256 _amountLD, // the amount, in Local Decimals, to be swapped
uint256 _minAmountLD // the minimum amount accepted out on destination
) external payable;
}
// SPDX-License-Identifier: BUSL-1.1
pragma solidity ^0.8.0;
interface IStargateToken {
event SendToChain(uint16 dstChainId, bytes to, uint256 qty);
function isMain() external returns(bool);
function sendTokens(
uint16 _dstChainId, // send tokens to this chainId
bytes calldata _to, // where to deliver the tokens on the destination chain
uint256 _qty, // how many tokens to send
address zroPaymentAddress, // ZRO payment address
bytes calldata adapterParam // txParameters
) external payable;
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
interface IERC20Usdt {
function totalSupply() external view returns (uint256);
function balanceOf(address account) external view returns (uint256);
function transfer(address recipient, uint256 amount) external;
function allowance(address owner, address spender) external view returns (uint256);
function approve(address spender, uint256 amount) external;
function transferFrom(address sender, address recipient, uint256 amount) external;
event Transfer(address indexed from, address indexed to, uint256 value);
event Approval(address indexed owner, address indexed spender, uint256 value);
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
library LibCache {
function set(
mapping(bytes32 => bytes32) storage _cache,
bytes32 _key,
bytes32 _value
) internal {
_cache[_key] = _value;
}
function setAddress(
mapping(bytes32 => bytes32) storage _cache,
bytes32 _key,
address _value
) internal {
_cache[_key] = bytes32(uint256(uint160(_value)));
}
function setUint256(
mapping(bytes32 => bytes32) storage _cache,
bytes32 _key,
uint256 _value
) internal {
_cache[_key] = bytes32(_value);
}
function getAddress(
mapping(bytes32 => bytes32) storage _cache,
bytes32 _key
) internal view returns (address ret) {
ret = address(uint160(uint256(_cache[_key])));
}
function getUint256(
mapping(bytes32 => bytes32) storage _cache,
bytes32 _key
) internal view returns (uint256 ret) {
ret = uint256(_cache[_key]);
}
function get(
mapping(bytes32 => bytes32) storage _cache,
bytes32 _key
) internal view returns (bytes32 ret) {
ret = _cache[_key];
}
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "../Config.sol";
library LibStack {
function setAddress(bytes32[] storage _stack, address _input) internal {
_stack.push(bytes32(uint256(uint160(_input))));
}
function set(bytes32[] storage _stack, bytes32 _input) internal {
_stack.push(_input);
}
function setHandlerType(
bytes32[] storage _stack,
Config.HandlerType _input
) internal {
_stack.push(bytes12(uint96(_input)));
}
function getAddress(
bytes32[] storage _stack
) internal returns (address ret) {
ret = address(uint160(uint256(peek(_stack))));
_stack.pop();
}
function getSig(bytes32[] storage _stack) internal returns (bytes4 ret) {
ret = bytes4(peek(_stack));
_stack.pop();
}
function get(bytes32[] storage _stack) internal returns (bytes32 ret) {
ret = peek(_stack);
_stack.pop();
}
function peek(
bytes32[] storage _stack
) internal view returns (bytes32 ret) {
uint256 length = _stack.length;
require(length > 0, "stack empty");
ret = _stack[length - 1];
}
function peek(
bytes32[] storage _stack,
uint256 _index
) internal view returns (bytes32 ret) {
uint256 length = _stack.length;
require(length > 0, "stack empty");
require(length > _index, "not enough elements in stack");
ret = _stack[length - _index - 1];
}
}