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// SPDX-License-Identifier: MIT | |
// modified version of OpenZeppelin Contract | |
pragma solidity ^0.8.0; | |
/** | |
* @dev Implementation of the {IERC20} interface. | |
*/ | |
contract BasicERC20 { | |
mapping(address => uint256) private _balances; | |
mapping(address => mapping(address => uint256)) private _allowances; | |
uint256 private _totalSupply; | |
/** | |
* @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 Mints the initial supply to the contract deployer. | |
*/ | |
constructor(uint256 initialSupply) { | |
_totalSupply = initialSupply; | |
_balances[msg.sender] = initialSupply; | |
} | |
/** | |
* @dev See {IERC20-totalSupply}. | |
*/ | |
function totalSupply() public view virtual returns (uint256) { | |
return _totalSupply; | |
} | |
/** | |
* @dev See {IERC20-balanceOf}. | |
*/ | |
function balanceOf(address account) public view virtual 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 returns (bool) { | |
address owner = msg.sender; | |
_transfer(owner, to, amount); | |
return true; | |
} | |
/** | |
* @dev See {IERC20-allowance}. | |
*/ | |
function allowance(address owner, address spender) public view virtual 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 returns (bool) { | |
address owner = msg.sender; | |
_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 returns (bool) { | |
address spender = msg.sender; | |
_spendAllowance(from, spender, amount); | |
_transfer(from, to, amount); | |
return true; | |
} | |
/** | |
* @dev Moves `amount` of tokens from `sender` to `recipient`. | |
* | |
* 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"); | |
uint256 fromBalance = _balances[from]; | |
require(fromBalance >= amount, "ERC20: transfer amount exceeds balance"); | |
unchecked { | |
_balances[from] = fromBalance - amount; | |
} | |
_balances[to] += amount; | |
emit Transfer(from, to, 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); | |
} | |
} | |
} | |
} |
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