contract Authorizable {

  address[] authorizers;
  mapping(address => uint) authorizerIndex;

  /**
   * @dev Throws if called by any account tat is not authorized. 
   */
  modifier onlyAuthorized {
    require(isAuthorized(msg.sender));
    _;
  }

  /**
   * @dev Contructor that authorizes the msg.sender. 
   */
  function Authorizable() public {
    authorizers.length = 2;
    authorizers[1] = msg.sender;
    authorizerIndex[msg.sender] = 1;
  }

  /**
   * @dev Function to get a specific authorizer
   * @param authorizerIndex index of the authorizer to be retrieved.
   * @return The address of the authorizer.
   */
  function getAuthorizer(uint authorizerIndex) external constant returns(address) {
    return address(authorizers[authorizerIndex + 1]);
  }

  /**
   * @dev Function to check if an address is authorized
   * @param _addr the address to check if it is authorized.
   * @return boolean flag if address is authorized.
   */
  function isAuthorized(address _addr) public constant returns(bool) {
    return authorizerIndex[_addr] > 0;
  }

  /**
   * @dev Function to add a new authorizer
   * @param _addr the address to add as a new authorizer.
   */
  function addAuthorized(address _addr) external onlyAuthorized {
    authorizerIndex[_addr] = authorizers.length;
    authorizers.length++;
    authorizers[authorizers.length - 1] = _addr;
  }

}
/**
 * @title Authorizable
 * @dev Allows to authorize access to certain function calls
 * 
 * ABI
 * [{"constant":true,"inputs":[{"name":"authorizerIndex","type":"uint256"}],"name":"getAuthorizer","outputs":[{"name":"","type":"address"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"_addr","type":"address"}],"name":"addAuthorized","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[{"name":"_addr","type":"address"}],"name":"isAuthorized","outputs":[{"name":"","type":"bool"}],"payable":false,"type":"function"},{"inputs":[],"payable":false,"type":"constructor"}]
 */
function Authorizable() public {
    authorizers.length = 2;
    authorizers[1] = msg.sender;
    authorizerIndex[msg.sender] = 1;
  }
/**
 * @dev Contructor that authorizes the msg.sender. 
 */