Contract Name:
Inscription
Contract Source Code:
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "./Logarithm.sol";
import "./TransferHelper.sol";
// This is common token interface, get balance of owner's token by ERC20/ERC721/ERC1155.
interface ICommonToken {
function balanceOf(address owner) external returns(uint256);
}
// This contract is extended from ERC20
contract Inscription is ERC20 {
using Logarithm for int256;
uint256 public cap; // Max amount
uint256 public limitPerMint; // Limitaion of each mint
uint256 public inscriptionId; // Inscription Id
uint256 public maxMintSize; // max mint size, that means the max mint quantity is: maxMintSize * limitPerMint
uint256 public freezeTime; // The frozen time (interval) between two mints is a fixed number of seconds. You can mint, but you will need to pay an additional mint fee, and this fee will be double for each mint.
address public onlyContractAddress; // Only addresses that hold these assets can mint
uint256 public onlyMinQuantity; // Only addresses that the quantity of assets hold more than this amount can mint
uint256 public baseFee; // base fee of the second mint after frozen interval. The first mint after frozen time is free.
uint256 public fundingCommission; // commission rate of fund raising, 100 means 1%
uint256 public crowdFundingRate; // rate of crowdfunding
address payable public crowdfundingAddress; // receiving fee of crowdfunding
address payable public inscriptionFactory;
mapping(address => uint256) public lastMintTimestamp; // record the last mint timestamp of account
mapping(address => uint256) public lastMintFee; // record the last mint fee
constructor(
string memory _name, // token name
string memory _tick, // token tick, same as symbol. must be 4 characters.
uint256 _cap, // Max amount
uint256 _limitPerMint, // Limitaion of each mint
uint256 _inscriptionId, // Inscription Id
uint256 _maxMintSize, // max mint size, that means the max mint quantity is: maxMintSize * limitPerMint. This is only availabe for non-frozen time token.
uint256 _freezeTime, // The frozen time (interval) between two mints is a fixed number of seconds. You can mint, but you will need to pay an additional mint fee, and this fee will be double for each mint.
address _onlyContractAddress, // Only addresses that hold these assets can mint
uint256 _onlyMinQuantity, // Only addresses that the quantity of assets hold more than this amount can mint
uint256 _baseFee, // base fee of the second mint after frozen interval. The first mint after frozen time is free.
uint256 _fundingCommission, // commission rate of fund raising, 100 means 1%
uint256 _crowdFundingRate, // rate of crowdfunding
address payable _crowdFundingAddress, // receiving fee of crowdfunding
address payable _inscriptionFactory
) ERC20(_name, _tick) {
require(_cap >= _limitPerMint, "Limit per mint exceed cap");
cap = _cap;
limitPerMint = _limitPerMint;
inscriptionId = _inscriptionId;
maxMintSize = _maxMintSize;
freezeTime = _freezeTime;
onlyContractAddress = _onlyContractAddress;
onlyMinQuantity = _onlyMinQuantity;
baseFee = _baseFee;
fundingCommission = _fundingCommission;
crowdFundingRate = _crowdFundingRate;
crowdfundingAddress = _crowdFundingAddress;
inscriptionFactory = _inscriptionFactory;
}
function mint(address _to) payable public {
// Check if the quantity after mint will exceed the cap
require(totalSupply() + limitPerMint <= cap, "Touched cap");
// Check if the assets in the msg.sender is satisfied
require(onlyContractAddress == address(0x0) || ICommonToken(onlyContractAddress).balanceOf(msg.sender) >= onlyMinQuantity, "You don't have required assets");
require(lastMintTimestamp[msg.sender] < block.timestamp, "Timestamp fail");
if(lastMintTimestamp[msg.sender] + freezeTime > block.timestamp) {
// The min extra tip is double of last mint fee
lastMintFee[msg.sender] = lastMintFee[msg.sender] == 0 ? baseFee : lastMintFee[msg.sender] * 2;
// Transfer the fee to the crowdfunding address
if(crowdFundingRate > 0) {
// Check if the tip is high than the min extra fee
require(msg.value >= crowdFundingRate + lastMintFee[msg.sender], "Send some ETH as fee and crowdfunding");
_dispatchFunding(crowdFundingRate);
}
// Transfer the tip to InscriptionFactory smart contract
if(msg.value - crowdFundingRate > 0) TransferHelper.safeTransferETH(inscriptionFactory, msg.value - crowdFundingRate);
// Do mint
_mint(_to, limitPerMint);
} else {
// Transfer the fee to the crowdfunding address
if(crowdFundingRate > 0) {
require(msg.value >= crowdFundingRate, "Send some ETH as crowdfunding");
_dispatchFunding(msg.value);
}
// Out of frozen time, free mint. Reset the timestamp and mint times.
lastMintFee[msg.sender] = 0;
lastMintTimestamp[msg.sender] = block.timestamp;
// Do mint
_mint(_to, limitPerMint);
}
}
// batch mint is only available for non-frozen-time tokens
function batchMint(address _to, uint256 _num) payable public {
require(_num <= maxMintSize, "exceed max mint size");
require(totalSupply() + _num * limitPerMint <= cap, "Touch cap");
require(freezeTime == 0, "Batch mint only for non-frozen token");
require(onlyContractAddress == address(0x0) || ICommonToken(onlyContractAddress).balanceOf(msg.sender) >= onlyMinQuantity, "You don't have required assets");
if(crowdFundingRate > 0) {
require(msg.value >= crowdFundingRate * _num, "Crowdfunding ETH not enough");
_dispatchFunding(msg.value);
}
for(uint256 i = 0; i < _num; i++) _mint(_to, limitPerMint);
}
function getMintFee(address _addr) public view returns(uint256 mintedTimes, uint256 nextMintFee) {
if(lastMintTimestamp[_addr] + freezeTime > block.timestamp) {
int256 scale = 1e18;
int256 halfScale = 5e17;
// times = log_2(lastMintFee / baseFee) + 1 (if lastMintFee > 0)
nextMintFee = lastMintFee[_addr] == 0 ? baseFee : lastMintFee[_addr] * 2;
mintedTimes = uint256((Logarithm.log2(int256(nextMintFee / baseFee) * scale, scale, halfScale) + 1) / scale) + 1;
}
}
function _dispatchFunding(uint256 _amount) private {
uint256 commission = _amount * fundingCommission / 10000;
TransferHelper.safeTransferETH(crowdfundingAddress, _amount - commission);
if(commission > 0) TransferHelper.safeTransferETH(inscriptionFactory, commission);
}
}
// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity >=0.6.0;
// helper methods for interacting with ERC20 tokens and sending ETH that do not consistently return true/false
library TransferHelper {
function safeApprove(
address token,
address to,
uint256 value
) internal {
// bytes4(keccak256(bytes('approve(address,uint256)')));
(bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x095ea7b3, to, value));
require(
success && (data.length == 0 || abi.decode(data, (bool))),
'TransferHelper::safeApprove: approve failed'
);
}
function safeTransfer(
address token,
address to,
uint256 value
) internal {
// bytes4(keccak256(bytes('transfer(address,uint256)')));
(bool success, bytes memory data) = token.call(abi.encodeWithSelector(0xa9059cbb, to, value));
require(
success && (data.length == 0 || abi.decode(data, (bool))),
'TransferHelper::safeTransfer: transfer failed'
);
}
function safeTransferFrom(
address token,
address from,
address to,
uint256 value
) internal {
// bytes4(keccak256(bytes('transferFrom(address,address,uint256)')));
(bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x23b872dd, from, to, value));
require(
success && (data.length == 0 || abi.decode(data, (bool))),
'TransferHelper::transferFrom: transferFrom failed'
);
}
function safeTransferETH(address to, uint256 value) internal {
(bool success, ) = to.call{value: value}(new bytes(0));
require(success, 'TransferHelper::safeTransferETH: ETH transfer failed');
}
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
library Logarithm {
/// @notice Finds the zero-based index of the first one in the binary representation of x.
/// @dev See the note on msb in the "Find First Set" Wikipedia article https://en.wikipedia.org/wiki/Find_first_set
/// @param x The uint256 number for which to find the index of the most significant bit.
/// @return msb The index of the most significant bit as an uint256.
function mostSignificantBit(uint256 x) internal pure returns (uint256 msb) {
if (x >= 2**128) {
x >>= 128;
msb += 128;
}
if (x >= 2**64) {
x >>= 64;
msb += 64;
}
if (x >= 2**32) {
x >>= 32;
msb += 32;
}
if (x >= 2**16) {
x >>= 16;
msb += 16;
}
if (x >= 2**8) {
x >>= 8;
msb += 8;
}
if (x >= 2**4) {
x >>= 4;
msb += 4;
}
if (x >= 2**2) {
x >>= 2;
msb += 2;
}
if (x >= 2**1) {
// No need to shift x any more.
msb += 1;
}
}
/// @notice Calculates the binary logarithm of x.
///
/// @dev Based on the iterative approximation algorithm.
/// https://en.wikipedia.org/wiki/Binary_logarithm#Iterative_approximation
///
/// Requirements:
/// - x must be greater than zero.
///
/// Caveats:
/// - The results are nor perfectly accurate to the last digit, due to the lossy precision of the iterative approximation.
///
/// @param x The signed 59.18-decimal fixed-point number for which to calculate the binary logarithm.
/// @return result The binary logarithm as a signed 59.18-decimal fixed-point number.
function log2(int256 x, int256 scale, int256 halfScale) internal pure returns (int256 result) {
require(x > 0);
unchecked {
// This works because log2(x) = -log2(1/x).
int256 sign;
if (x >= scale) {
sign = 1;
} else {
sign = -1;
// Do the fixed-point inversion inline to save gas. The numerator is SCALE * SCALE.
assembly {
x := div(1000000000000000000000000000000000000, x)
}
}
// Calculate the integer part of the logarithm and add it to the result and finally calculate y = x * 2^(-n).
uint256 n = mostSignificantBit(uint256(x / scale));
// The integer part of the logarithm as a signed 59.18-decimal fixed-point number. The operation can't overflow
// because n is maximum 255, SCALE is 1e18 and sign is either 1 or -1.
result = int256(n) * scale;
// This is y = x * 2^(-n).
int256 y = x >> n;
// If y = 1, the fractional part is zero.
if (y == scale) {
return result * sign;
}
// Calculate the fractional part via the iterative approximation.
// The "delta >>= 1" part is equivalent to "delta /= 2", but shifting bits is faster.
for (int256 delta = int256(halfScale); delta > 0; delta >>= 1) {
y = (y * y) / scale;
// Is y^2 > 2 and so in the range [2,4)?
if (y >= 2 * scale) {
// Add the 2^(-m) factor to the logarithm.
result += delta;
// Corresponds to z/2 on Wikipedia.
y >>= 1;
}
}
result *= sign;
}
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/ERC20.sol)
pragma solidity ^0.8.0;
import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.sol";
/**
* @dev Implementation of the {IERC20} interface.
*
* This implementation is agnostic to the way tokens are created. This means
* that a supply mechanism has to be added in a derived contract using {_mint}.
* For a generic mechanism see {ERC20PresetMinterPauser}.
*
* TIP: For a detailed writeup see our guide
* https://forum.openzeppelin.com/t/how-to-implement-erc20-supply-mechanisms/226[How
* to implement supply mechanisms].
*
* The default value of {decimals} is 18. To change this, you should override
* this function so it returns a different value.
*
* We have followed general OpenZeppelin Contracts guidelines: functions revert
* instead returning `false` on failure. This behavior is nonetheless
* conventional and does not conflict with the expectations of ERC20
* applications.
*
* Additionally, an {Approval} event is emitted on calls to {transferFrom}.
* This allows applications to reconstruct the allowance for all accounts just
* by listening to said events. Other implementations of the EIP may not emit
* these events, as it isn't required by the specification.
*
* Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
* functions have been added to mitigate the well-known issues around setting
* allowances. See {IERC20-approve}.
*/
contract ERC20 is Context, IERC20, IERC20Metadata {
mapping(address => uint256) private _balances;
mapping(address => mapping(address => uint256)) private _allowances;
uint256 private _totalSupply;
string private _name;
string private _symbol;
/**
* @dev Sets the values for {name} and {symbol}.
*
* All two of these values are immutable: they can only be set once during
* construction.
*/
constructor(string memory name_, string memory symbol_) {
_name = name_;
_symbol = symbol_;
}
/**
* @dev Returns the name of the token.
*/
function name() public view virtual override returns (string memory) {
return _name;
}
/**
* @dev Returns the symbol of the token, usually a shorter version of the
* name.
*/
function symbol() public view virtual override returns (string memory) {
return _symbol;
}
/**
* @dev Returns the number of decimals used to get its user representation.
* For example, if `decimals` equals `2`, a balance of `505` tokens should
* be displayed to a user as `5.05` (`505 / 10 ** 2`).
*
* Tokens usually opt for a value of 18, imitating the relationship between
* Ether and Wei. This is the default value returned by this function, unless
* it's overridden.
*
* NOTE: This information is only used for _display_ purposes: it in
* no way affects any of the arithmetic of the contract, including
* {IERC20-balanceOf} and {IERC20-transfer}.
*/
function decimals() public view virtual override returns (uint8) {
return 18;
}
/**
* @dev See {IERC20-totalSupply}.
*/
function totalSupply() public view virtual override returns (uint256) {
return _totalSupply;
}
/**
* @dev See {IERC20-balanceOf}.
*/
function balanceOf(address account) public view virtual override returns (uint256) {
return _balances[account];
}
/**
* @dev See {IERC20-transfer}.
*
* Requirements:
*
* - `to` cannot be the zero address.
* - the caller must have a balance of at least `amount`.
*/
function transfer(address to, uint256 amount) public virtual override returns (bool) {
address owner = _msgSender();
_transfer(owner, to, amount);
return true;
}
/**
* @dev See {IERC20-allowance}.
*/
function allowance(address owner, address spender) public view virtual override returns (uint256) {
return _allowances[owner][spender];
}
/**
* @dev See {IERC20-approve}.
*
* NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
* `transferFrom`. This is semantically equivalent to an infinite approval.
*
* Requirements:
*
* - `spender` cannot be the zero address.
*/
function approve(address spender, uint256 amount) public virtual override returns (bool) {
address owner = _msgSender();
_approve(owner, spender, amount);
return true;
}
/**
* @dev See {IERC20-transferFrom}.
*
* Emits an {Approval} event indicating the updated allowance. This is not
* required by the EIP. See the note at the beginning of {ERC20}.
*
* NOTE: Does not update the allowance if the current allowance
* is the maximum `uint256`.
*
* Requirements:
*
* - `from` and `to` cannot be the zero address.
* - `from` must have a balance of at least `amount`.
* - the caller must have allowance for ``from``'s tokens of at least
* `amount`.
*/
function transferFrom(address from, address to, uint256 amount) public virtual override returns (bool) {
address spender = _msgSender();
_spendAllowance(from, spender, amount);
_transfer(from, to, amount);
return true;
}
/**
* @dev Atomically increases the allowance granted to `spender` by the caller.
*
* This is an alternative to {approve} that can be used as a mitigation for
* problems described in {IERC20-approve}.
*
* Emits an {Approval} event indicating the updated allowance.
*
* Requirements:
*
* - `spender` cannot be the zero address.
*/
function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
address owner = _msgSender();
_approve(owner, spender, allowance(owner, spender) + addedValue);
return true;
}
/**
* @dev Atomically decreases the allowance granted to `spender` by the caller.
*
* This is an alternative to {approve} that can be used as a mitigation for
* problems described in {IERC20-approve}.
*
* Emits an {Approval} event indicating the updated allowance.
*
* Requirements:
*
* - `spender` cannot be the zero address.
* - `spender` must have allowance for the caller of at least
* `subtractedValue`.
*/
function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
address owner = _msgSender();
uint256 currentAllowance = allowance(owner, spender);
require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
unchecked {
_approve(owner, spender, currentAllowance - subtractedValue);
}
return true;
}
/**
* @dev Moves `amount` of tokens from `from` to `to`.
*
* This internal function is equivalent to {transfer}, and can be used to
* e.g. implement automatic token fees, slashing mechanisms, etc.
*
* Emits a {Transfer} event.
*
* Requirements:
*
* - `from` cannot be the zero address.
* - `to` cannot be the zero address.
* - `from` must have a balance of at least `amount`.
*/
function _transfer(address from, address to, uint256 amount) internal virtual {
require(from != address(0), "ERC20: transfer from the zero address");
require(to != address(0), "ERC20: transfer to the zero address");
_beforeTokenTransfer(from, to, amount);
uint256 fromBalance = _balances[from];
require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
unchecked {
_balances[from] = fromBalance - amount;
// Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
// decrementing then incrementing.
_balances[to] += amount;
}
emit Transfer(from, to, amount);
_afterTokenTransfer(from, to, amount);
}
/** @dev Creates `amount` tokens and assigns them to `account`, increasing
* the total supply.
*
* Emits a {Transfer} event with `from` set to the zero address.
*
* Requirements:
*
* - `account` cannot be the zero address.
*/
function _mint(address account, uint256 amount) internal virtual {
require(account != address(0), "ERC20: mint to the zero address");
_beforeTokenTransfer(address(0), account, amount);
_totalSupply += amount;
unchecked {
// Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
_balances[account] += amount;
}
emit Transfer(address(0), account, amount);
_afterTokenTransfer(address(0), account, amount);
}
/**
* @dev Destroys `amount` tokens from `account`, reducing the
* total supply.
*
* Emits a {Transfer} event with `to` set to the zero address.
*
* Requirements:
*
* - `account` cannot be the zero address.
* - `account` must have at least `amount` tokens.
*/
function _burn(address account, uint256 amount) internal virtual {
require(account != address(0), "ERC20: burn from the zero address");
_beforeTokenTransfer(account, address(0), amount);
uint256 accountBalance = _balances[account];
require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
unchecked {
_balances[account] = accountBalance - amount;
// Overflow not possible: amount <= accountBalance <= totalSupply.
_totalSupply -= amount;
}
emit Transfer(account, address(0), amount);
_afterTokenTransfer(account, address(0), amount);
}
/**
* @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
*
* This internal function is equivalent to `approve`, and can be used to
* e.g. set automatic allowances for certain subsystems, etc.
*
* Emits an {Approval} event.
*
* Requirements:
*
* - `owner` cannot be the zero address.
* - `spender` cannot be the zero address.
*/
function _approve(address owner, address spender, uint256 amount) internal virtual {
require(owner != address(0), "ERC20: approve from the zero address");
require(spender != address(0), "ERC20: approve to the zero address");
_allowances[owner][spender] = amount;
emit Approval(owner, spender, amount);
}
/**
* @dev Updates `owner` s allowance for `spender` based on spent `amount`.
*
* Does not update the allowance amount in case of infinite allowance.
* Revert if not enough allowance is available.
*
* Might emit an {Approval} event.
*/
function _spendAllowance(address owner, address spender, uint256 amount) internal virtual {
uint256 currentAllowance = allowance(owner, spender);
if (currentAllowance != type(uint256).max) {
require(currentAllowance >= amount, "ERC20: insufficient allowance");
unchecked {
_approve(owner, spender, currentAllowance - amount);
}
}
}
/**
* @dev Hook that is called before any transfer of tokens. This includes
* minting and burning.
*
* Calling conditions:
*
* - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
* will be transferred to `to`.
* - when `from` is zero, `amount` tokens will be minted for `to`.
* - when `to` is zero, `amount` of ``from``'s tokens will be burned.
* - `from` and `to` are never both zero.
*
* To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
*/
function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual {}
/**
* @dev Hook that is called after any transfer of tokens. This includes
* minting and burning.
*
* Calling conditions:
*
* - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
* has been transferred to `to`.
* - when `from` is zero, `amount` tokens have been minted for `to`.
* - when `to` is zero, `amount` of ``from``'s tokens have been burned.
* - `from` and `to` are never both zero.
*
* To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
*/
function _afterTokenTransfer(address from, address to, uint256 amount) internal virtual {}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)
pragma solidity ^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.
*/
abstract contract Context {
function _msgSender() internal view virtual returns (address) {
return msg.sender;
}
function _msgData() internal view virtual returns (bytes calldata) {
return msg.data;
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)
pragma solidity ^0.8.0;
import "../IERC20.sol";
/**
* @dev Interface for the optional metadata functions from the ERC20 standard.
*
* _Available since v4.1._
*/
interface IERC20Metadata is IERC20 {
/**
* @dev Returns the name of the token.
*/
function name() external view returns (string memory);
/**
* @dev Returns the symbol of the token.
*/
function symbol() external view returns (string memory);
/**
* @dev Returns the decimals places of the token.
*/
function decimals() external view returns (uint8);
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/IERC20.sol)
pragma solidity ^0.8.0;
/**
* @dev Interface of the ERC20 standard as defined in the EIP.
*/
interface IERC20 {
/**
* @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);
/**
* @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 `to`.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a {Transfer} event.
*/
function transfer(address to, 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 `from` to `to` 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 from, address to, uint256 amount) external returns (bool);
}