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- pragma solidity ^0.5.0;
- import "./IERC20.sol";
- import "../../math/SafeMath.sol";
- /**
- * @title Standard ERC20 token
- *
- * @dev Implementation of the basic standard token.
- * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md
- * Originally based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
- *
- * This implementation emits additional Approval events, allowing applications to reconstruct the allowance status for
- * all accounts just by listening to said events. Note that this isn't required by the specification, and other
- * compliant implementations may not do it.
- */
- contract ERC20 is IERC20 {
- using SafeMath for uint256;
- mapping (address => uint256) private _balances;
- mapping (address => mapping (address => uint256)) private _allowed;
- uint256 private _totalSupply;
- /**
- * @dev Total number of tokens in existence
- */
- function totalSupply() public view returns (uint256) {
- return _totalSupply;
- }
- /**
- * @dev Gets the balance of the specified address.
- * @param owner The address to query the balance of.
- * @return An uint256 representing the amount owned by the passed address.
- */
- function balanceOf(address owner) public view returns (uint256) {
- return _balances[owner];
- }
- /**
- * @dev Function to check the amount of tokens that an owner allowed to a spender.
- * @param owner address The address which owns the funds.
- * @param spender address The address which will spend the funds.
- * @return A uint256 specifying the amount of tokens still available for the spender.
- */
- function allowance(address owner, address spender) public view returns (uint256) {
- return _allowed[owner][spender];
- }
- /**
- * @dev Transfer token for a specified address
- * @param to The address to transfer to.
- * @param value The amount to be transferred.
- */
- function transfer(address to, uint256 value) public returns (bool) {
- _transfer(msg.sender, to, value);
- return true;
- }
- /**
- * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
- * 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
- * @param spender The address which will spend the funds.
- * @param value The amount of tokens to be spent.
- */
- function approve(address spender, uint256 value) public returns (bool) {
- require(spender != address(0));
- _allowed[msg.sender][spender] = value;
- emit Approval(msg.sender, spender, value);
- return true;
- }
- /**
- * @dev Transfer tokens from one address to another.
- * Note that while this function emits an Approval event, this is not required as per the specification,
- * and other compliant implementations may not emit the event.
- * @param from address The address which you want to send tokens from
- * @param to address The address which you want to transfer to
- * @param value uint256 the amount of tokens to be transferred
- */
- function transferFrom(address from, address to, uint256 value) public returns (bool) {
- _allowed[from][msg.sender] = _allowed[from][msg.sender].sub(value);
- _transfer(from, to, value);
- emit Approval(from, msg.sender, _allowed[from][msg.sender]);
- return true;
- }
- /**
- * @dev Increase the amount of tokens that an owner allowed to a spender.
- * approve should be called when allowed_[_spender] == 0. To increment
- * allowed value is better to use this function to avoid 2 calls (and wait until
- * the first transaction is mined)
- * From MonolithDAO Token.sol
- * Emits an Approval event.
- * @param spender The address which will spend the funds.
- * @param addedValue The amount of tokens to increase the allowance by.
- */
- function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
- require(spender != address(0));
- _allowed[msg.sender][spender] = _allowed[msg.sender][spender].add(addedValue);
- emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
- return true;
- }
- /**
- * @dev Decrease the amount of tokens that an owner allowed to a spender.
- * approve should be called when allowed_[_spender] == 0. To decrement
- * allowed value is better to use this function to avoid 2 calls (and wait until
- * the first transaction is mined)
- * From MonolithDAO Token.sol
- * Emits an Approval event.
- * @param spender The address which will spend the funds.
- * @param subtractedValue The amount of tokens to decrease the allowance by.
- */
- function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
- require(spender != address(0));
- _allowed[msg.sender][spender] = _allowed[msg.sender][spender].sub(subtractedValue);
- emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
- return true;
- }
- /**
- * @dev Transfer token for a specified addresses
- * @param from The address to transfer from.
- * @param to The address to transfer to.
- * @param value The amount to be transferred.
- */
- function _transfer(address from, address to, uint256 value) internal {
- require(to != address(0));
- _balances[from] = _balances[from].sub(value);
- _balances[to] = _balances[to].add(value);
- emit Transfer(from, to, value);
- }
- /**
- * @dev Internal function that mints an amount of the token and assigns it to
- * an account. This encapsulates the modification of balances such that the
- * proper events are emitted.
- * @param account The account that will receive the created tokens.
- * @param value The amount that will be created.
- */
- function _mint(address account, uint256 value) internal {
- require(account != address(0));
- _totalSupply = _totalSupply.add(value);
- _balances[account] = _balances[account].add(value);
- emit Transfer(address(0), account, value);
- }
- /**
- * @dev Internal function that burns an amount of the token of a given
- * account.
- * @param account The account whose tokens will be burnt.
- * @param value The amount that will be burnt.
- */
- function _burn(address account, uint256 value) internal {
- require(account != address(0));
- _totalSupply = _totalSupply.sub(value);
- _balances[account] = _balances[account].sub(value);
- emit Transfer(account, address(0), value);
- }
- /**
- * @dev Internal function that burns an amount of the token of a given
- * account, deducting from the sender's allowance for said account. Uses the
- * internal burn function.
- * Emits an Approval event (reflecting the reduced allowance).
- * @param account The account whose tokens will be burnt.
- * @param value The amount that will be burnt.
- */
- function _burnFrom(address account, uint256 value) internal {
- _allowed[account][msg.sender] = _allowed[account][msg.sender].sub(value);
- _burn(account, value);
- emit Approval(account, msg.sender, _allowed[account][msg.sender]);
- }
- }
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