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March 6, 2018 ยท View on GitHub
pragma solidity ^0.4.18;
/**
- @title SafeMath
- @dev Math operations with safety checks that throw on error */ library SafeMath {
/**
- @dev Multiplies two numbers, throws on overflow. */ function mul(uint256 a, uint256 b) internal pure returns (uint256) { if (a == 0) { return 0; } uint256 c = a * b; assert(c / a == b); return c; }
/**
- @dev Integer division of two numbers, truncating the quotient. */ function div(uint256 a, uint256 b) internal pure returns (uint256) { // assert(b > 0); // Solidity automatically throws when dividing by 0 uint256 c = a / b; // assert(a == b * c + a % b); // There is no case in which this doesn't hold return c; }
/**
- @dev Substracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend). */ function sub(uint256 a, uint256 b) internal pure returns (uint256) { assert(b <= a); return a - b; }
/**
- @dev Adds two numbers, throws on overflow. */ function add(uint256 a, uint256 b) internal pure returns (uint256) { uint256 c = a + b; assert(c >= a); return c; } }
/**
- @title ERC20Basic
- @dev Simpler version of ERC20 interface
- @dev see https://github.com/ethereum/EIPs/issues/179 */ contract ERC20Basic { function totalSupply() public view returns (uint256); function balanceOf(address who) public view returns (uint256); function transfer(address to, uint256 value) public returns (bool); event Transfer(address indexed from, address indexed to, uint256 value); }
/**
- @title ERC20 interface
- @dev see https://github.com/ethereum/EIPs/issues/20 */ contract ERC20 is ERC20Basic { function allowance(address owner, address spender) public view returns (uint256); function transferFrom(address from, address to, uint256 value) public returns (bool); function approve(address spender, uint256 value) public returns (bool); event Approval(address indexed owner, address indexed spender, uint256 value); }
/**
- @title Basic token
- @dev Basic version of StandardToken, with no allowances. */ contract BasicToken is ERC20Basic { using SafeMath for uint256;
mapping(address => uint256) balances;
uint256 totalSupply_;
/**
- @dev total number of tokens in existence */ function totalSupply() public view returns (uint256) { return totalSupply_; }
/**
-
@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) { require(_to != address(0)); require(_value <= balances[msg.sender]);
// SafeMath.sub will throw if there is not enough balance. balances[msg.sender] = balances[msg.sender].sub(_value); balances[_to] = balances[_to].add(_value); Transfer(msg.sender, _to, _value); return true; }
/**
- @dev Gets the balance of the specified address.
- @param _owner The address to query the the balance of.
- @return An uint256 representing the amount owned by the passed address. */ function balanceOf(address _owner) public view returns (uint256 balance) { return balances[_owner]; }
}
/**
- @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; }
}