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March 13, 2020 01:53
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ERC20 from OpenZeppelin (Solidity 0.4.24)
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pragma solidity ^0.4.24; | |
/** | |
* @dev Interface of the ERC20 standard as defined in the EIP. Does not include | |
* the optional functions; to access them see `ERC20Detailed`. | |
*/ | |
interface IERC20 { | |
function totalSupply() external view returns (uint256); | |
function balanceOf(address account) external view returns (uint256); | |
function transfer(address recipient, uint256 amount) external returns (bool); | |
function allowance(address owner, address spender) external view returns (uint256); | |
function approve(address spender, uint256 amount) external returns (bool); | |
function transferFrom(address sender, address recipient, uint256 amount) external returns (bool); | |
event Transfer(address indexed from, address indexed to, uint256 value); | |
event Approval(address indexed owner, address indexed spender, uint256 value); | |
} | |
library SafeMath { | |
/** | |
* @dev Returns the addition of two unsigned integers, reverting on | |
* overflow. | |
* | |
* Counterpart to Solidity's `+` operator. | |
* | |
* Requirements: | |
* - Addition cannot overflow. | |
*/ | |
function add(uint256 a, uint256 b) internal pure returns (uint256) { | |
uint256 c = a + b; | |
require(c >= a, "SafeMath: addition overflow"); | |
return c; | |
} | |
/** | |
* @dev Returns the subtraction of two unsigned integers, reverting on | |
* overflow (when the result is negative). | |
* | |
* Counterpart to Solidity's `-` operator. | |
* | |
* Requirements: | |
* - Subtraction cannot overflow. | |
*/ | |
function sub(uint256 a, uint256 b) internal pure returns (uint256) { | |
require(b <= a, "SafeMath: subtraction overflow"); | |
uint256 c = a - b; | |
return c; | |
} | |
/** | |
* @dev Returns the multiplication of two unsigned integers, reverting on | |
* overflow. | |
* | |
* Counterpart to Solidity's `*` operator. | |
* | |
* Requirements: | |
* - Multiplication cannot overflow. | |
*/ | |
function mul(uint256 a, uint256 b) internal pure returns (uint256) { | |
// Gas optimization: this is cheaper than requiring 'a' not being zero, but the | |
// benefit is lost if 'b' is also tested. | |
// See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522 | |
if (a == 0) { | |
return 0; | |
} | |
uint256 c = a * b; | |
require(c / a == b, "SafeMath: multiplication overflow"); | |
return c; | |
} | |
/** | |
* @dev Returns the integer division of two unsigned integers. Reverts on | |
* division by zero. The result is rounded towards zero. | |
* | |
* Counterpart to Solidity's `/` operator. Note: this function uses a | |
* `revert` opcode (which leaves remaining gas untouched) while Solidity | |
* uses an invalid opcode to revert (consuming all remaining gas). | |
* | |
* Requirements: | |
* - The divisor cannot be zero. | |
*/ | |
function div(uint256 a, uint256 b) internal pure returns (uint256) { | |
// Solidity only automatically asserts when dividing by 0 | |
require(b > 0, "SafeMath: division by zero"); | |
uint256 c = a / b; | |
// assert(a == b * c + a % b); // There is no case in which this doesn't hold | |
return c; | |
} | |
/** | |
* @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo), | |
* Reverts when dividing by zero. | |
* | |
* Counterpart to Solidity's `%` operator. This function uses a `revert` | |
* opcode (which leaves remaining gas untouched) while Solidity uses an | |
* invalid opcode to revert (consuming all remaining gas). | |
* | |
* Requirements: | |
* - The divisor cannot be zero. | |
*/ | |
function mod(uint256 a, uint256 b) internal pure returns (uint256) { | |
require(b != 0, "SafeMath: modulo by zero"); | |
return a % b; | |
} | |
} | |
/** | |
* @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 `ERC20Mintable`. | |
* | |
* *For a detailed writeup see our guide [How to implement supply | |
* mechanisms](https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226).* | |
* | |
* We have followed general OpenZeppelin guidelines: functions revert instead | |
* of 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 MyERC20 is IERC20 { | |
using SafeMath for uint256; | |
mapping (address => uint256) private _balances; | |
mapping (address => mapping (address => uint256)) private _allowances; | |
// NOTE Start of https://github.com/OpenZeppelin/openzeppelin-solidity/blob/v2.3.0/contracts/token/ERC20/ERC20Detailed.sol | |
string private _name; | |
string private _symbol; | |
uint8 private _decimals; | |
constructor (string memory name, string memory symbol, uint8 decimals) public { | |
_name = name; | |
_symbol = symbol; | |
_decimals = decimals; | |
_mint(msg.sender, 100000 * 10 ** uint256(decimals)); // CAUTION! | |
} | |
/** | |
* @dev Returns the name of the token. | |
*/ | |
function name() public view returns (string memory) { | |
return _name; | |
} | |
/** | |
* @dev Returns the symbol of the token, usually a shorter version of the | |
* name. | |
*/ | |
function symbol() public view 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. | |
* | |
* > Note that 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 returns (uint8) { | |
return _decimals; | |
} | |
// NOTE End of https://github.com/OpenZeppelin/openzeppelin-solidity/blob/v2.3.0/contracts/token/ERC20/ERC20Detailed.sol | |
uint256 private _totalSupply; | |
/** | |
* @dev See `IERC20.totalSupply`. | |
*/ | |
function totalSupply() public view returns (uint256) { | |
return _totalSupply; | |
} | |
/** | |
* @dev See `IERC20.balanceOf`. | |
*/ | |
function balanceOf(address account) public view returns (uint256) { | |
return _balances[account]; | |
} | |
/** | |
* @dev See `IERC20.transfer`. | |
* | |
* Requirements: | |
* | |
* - `recipient` cannot be the zero address. | |
* - the caller must have a balance of at least `amount`. | |
*/ | |
function transfer(address recipient, uint256 amount) public returns (bool) { | |
_transfer(msg.sender, recipient, amount); | |
return true; | |
} | |
/** | |
* @dev See `IERC20.allowance`. | |
*/ | |
function allowance(address owner, address spender) public view returns (uint256) { | |
return _allowances[owner][spender]; | |
} | |
/** | |
* @dev See `IERC20.approve`. | |
* | |
* Requirements: | |
* | |
* - `spender` cannot be the zero address. | |
*/ | |
function approve(address spender, uint256 value) public returns (bool) { | |
_approve(msg.sender, spender, value); | |
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`; | |
* | |
* Requirements: | |
* - `sender` and `recipient` cannot be the zero address. | |
* - `sender` must have a balance of at least `value`. | |
* - the caller must have allowance for `sender`'s tokens of at least | |
* `amount`. | |
*/ | |
function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) { | |
_transfer(sender, recipient, amount); | |
_approve(sender, msg.sender, _allowances[sender][msg.sender].sub(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 returns (bool) { | |
_approve(msg.sender, spender, _allowances[msg.sender][spender].add(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 returns (bool) { | |
_approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue)); | |
return true; | |
} | |
/** | |
* @dev Moves tokens `amount` from `sender` to `recipient`. | |
* | |
* This is 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: | |
* | |
* - `sender` cannot be the zero address. | |
* - `recipient` cannot be the zero address. | |
* - `sender` must have a balance of at least `amount`. | |
*/ | |
function _transfer(address sender, address recipient, uint256 amount) internal { | |
require(sender != address(0), "ERC20: transfer from the zero address"); | |
require(recipient != address(0), "ERC20: transfer to the zero address"); | |
_balances[sender] = _balances[sender].sub(amount); | |
_balances[recipient] = _balances[recipient].add(amount); | |
emit Transfer(sender, recipient, 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 | |
* | |
* - `to` cannot be the zero address. | |
*/ | |
function _mint(address account, uint256 amount) internal { | |
require(account != address(0), "ERC20: mint to the zero address"); | |
_totalSupply = _totalSupply.add(amount); | |
_balances[account] = _balances[account].add(amount); | |
emit Transfer(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 value) internal { | |
require(account != address(0), "ERC20: burn from the zero address"); | |
_totalSupply = _totalSupply.sub(value); | |
_balances[account] = _balances[account].sub(value); | |
emit Transfer(account, address(0), value); | |
} | |
/** | |
* @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens. | |
* | |
* This is 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 value) internal { | |
require(owner != address(0), "ERC20: approve from the zero address"); | |
require(spender != address(0), "ERC20: approve to the zero address"); | |
_allowances[owner][spender] = value; | |
emit Approval(owner, spender, value); | |
} | |
/** | |
* @dev Destoys `amount` tokens from `account`.`amount` is then deducted | |
* from the caller's allowance. | |
* | |
* See `_burn` and `_approve`. | |
*/ | |
function _burnFrom(address account, uint256 amount) internal { | |
_burn(account, amount); | |
_approve(account, msg.sender, _allowances[account][msg.sender].sub(amount)); | |
} | |
function approveTest(address spender, uint256 value) public returns (address, address, uint256) { | |
_allowances[msg.sender][spender] = value; | |
return (msg.sender, spender, _allowances[msg.sender][spender]); | |
} | |
} |
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