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127 lines
4.0 KiB
127 lines
4.0 KiB
pragma solidity ^0.4.24;
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import "./BasicToken.sol";
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import "./ERC20.sol";
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/**
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* @title Standard ERC20 token
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*
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* @dev Implementation of the basic standard token.
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* @dev https://github.com/ethereum/EIPs/issues/20
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* @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
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*/
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contract StandardToken is ERC20, BasicToken {
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mapping (address => mapping (address => uint256)) internal allowed;
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/**
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* @dev Transfer tokens from one address to another
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* @param _from address The address which you want to send tokens from
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* @param _to address The address which you want to transfer to
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* @param _value uint256 the amount of tokens to be transferred
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*/
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function transferFrom(
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address _from,
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address _to,
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uint256 _value
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)
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public
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returns (bool)
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{
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require(_to != address(0));
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require(_value <= balances[_from]);
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require(_value <= allowed[_from][msg.sender]);
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balances[_from] = balances[_from].sub(_value);
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balances[_to] = balances[_to].add(_value);
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allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
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emit Transfer(_from, _to, _value);
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return true;
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}
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/**
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* @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
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*
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* Beware that changing an allowance with this method brings the risk that someone may use both the old
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* and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
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* race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
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* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
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* @param _spender The address which will spend the funds.
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* @param _value The amount of tokens to be spent.
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*/
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function approve(address _spender, uint256 _value) public returns (bool) {
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allowed[msg.sender][_spender] = _value;
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emit Approval(msg.sender, _spender, _value);
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return true;
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}
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/**
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* @dev Function to check the amount of tokens that an owner allowed to a spender.
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* @param _owner address The address which owns the funds.
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* @param _spender address The address which will spend the funds.
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* @return A uint256 specifying the amount of tokens still available for the spender.
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*/
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function allowance(
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address _owner,
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address _spender
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)
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public
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view
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returns (uint256)
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{
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return allowed[_owner][_spender];
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}
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/**
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* @dev Increase the amount of tokens that an owner allowed to a spender.
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*
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* approve should be called when allowed[_spender] == 0. To increment
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* allowed value is better to use this function to avoid 2 calls (and wait until
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* the first transaction is mined)
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* From MonolithDAO Token.sol
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* @param _spender The address which will spend the funds.
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* @param _addedValue The amount of tokens to increase the allowance by.
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*/
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function increaseApproval(
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address _spender,
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uint256 _addedValue
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)
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public
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returns (bool)
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{
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allowed[msg.sender][_spender] = (
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allowed[msg.sender][_spender].add(_addedValue));
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emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
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return true;
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}
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/**
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* @dev Decrease the amount of tokens that an owner allowed to a spender.
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*
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* approve should be called when allowed[_spender] == 0. To decrement
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* allowed value is better to use this function to avoid 2 calls (and wait until
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* the first transaction is mined)
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* From MonolithDAO Token.sol
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* @param _spender The address which will spend the funds.
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* @param _subtractedValue The amount of tokens to decrease the allowance by.
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*/
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function decreaseApproval(
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address _spender,
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uint256 _subtractedValue
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)
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public
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returns (bool)
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{
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uint256 oldValue = allowed[msg.sender][_spender];
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if (_subtractedValue > oldValue) {
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allowed[msg.sender][_spender] = 0;
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} else {
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allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
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}
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emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
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return true;
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}
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}
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