openzeppelin-contracts/contracts/BaseToken.sol

pragma solidity ^0.4.0;

// Everything throws instead of returning false on failure.
import './ERC20.sol';

/**
 * ERC 20 token
 *
 * https://github.com/ethereum/EIPs/issues/20
 * Based on code by FirstBlood:
 * https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
contract BaseToken is ERC20 {

  mapping(address => uint256) balances;
  mapping (address => mapping (address => uint256)) allowed;
  uint256 public totalSupply;


  function transfer(address _to, uint256 _value) returns (bool success) {
    if (balances[msg.sender] >= _value &&
        balances[_to] + _value > balances[_to]) {
      balances[msg.sender] -= _value;
      balances[_to] += _value;
      Transfer(msg.sender, _to, _value);
      return true;
    } else { return false; }
  }

  function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
    if (balances[_from] >= _value &&
        allowed[_from][msg.sender] >= _value &&
        balances[_to] + _value > balances[_to]) {
      balances[_to] += _value;
      balances[_from] -= _value;
      allowed[_from][msg.sender] -= _value;
      Transfer(_from, _to, _value);
      return true;
    } else { return false; }
  }

  function balanceOf(address _owner) constant returns (uint256 balance) {
    return balances[_owner];
  }

  function approve(address _spender, uint256 _value) returns (bool success) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;
  }

  function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
    return allowed[_owner][_spender];
  }

}