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- pragma solidity ^0.4.18;
- import "./BasicToken.sol";
- import "./ERC20.sol";
- /**
- * @title Standard ERC20 token
- *
- * @dev Implementation of the basic standard token.
- * @dev https://github.com/ethereum/EIPs/issues/20
- * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
- */
- contract StandardToken is ERC20, BasicToken {
- mapping (address => mapping (address => uint256)) internal allowed;
- /**
- * @dev Transfer tokens from one address to another
- * @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) {
- require(_to != address(0));
- require(_value <= balances[_from]);
- require(_value <= allowed[_from][msg.sender]);
- balances[_from] = balances[_from].sub(_value);
- balances[_to] = balances[_to].add(_value);
- allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
- Transfer(_from, _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) {
- allowed[msg.sender][_spender] = _value;
- Approval(msg.sender, _spender, _value);
- return true;
- }
- /**
- * @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 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
- * @param _spender The address which will spend the funds.
- * @param _addedValue The amount of tokens to increase the allowance by.
- */
- function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
- allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
- 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
- * @param _spender The address which will spend the funds.
- * @param _subtractedValue The amount of tokens to decrease the allowance by.
- */
- function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
- uint oldValue = allowed[msg.sender][_spender];
- if (_subtractedValue > oldValue) {
- allowed[msg.sender][_spender] = 0;
- } else {
- allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
- }
- Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
- return true;
- }
- }
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