Address Details

contract

pragma solidity ^0.5.13;
pragma experimental ABIEncoderV2;

import { Ownable } from "openzeppelin-solidity/contracts/ownership/Ownable.sol";
import { SafeMath } from "openzeppelin-solidity/contracts/math/SafeMath.sol";

import { IExchangeProvider } from "./interfaces/IExchangeProvider.sol";
import { IBiPoolManager } from "./interfaces/IBiPoolManager.sol";
import { IReserve } from "./interfaces/IReserve.sol";
import { IPricingModule } from "./interfaces/IPricingModule.sol";
import { ISortedOracles } from "./interfaces/ISortedOracles.sol";

import { StableToken } from "./StableToken.sol";

import { Initializable } from "./common/Initializable.sol";
import { FixidityLib } from "./common/FixidityLib.sol";

// TODO: Remove when migrating to mento-core. Newer versions of OZ-contracts have this interface
interface IERC20Metadata {
  function symbol() external view returns (string memory);
}

/**
 * @title BiPoolExchangeManager
 * @notice An exchange manager that manages asset exchanges consisting of two assets
 */
contract BiPoolManager is IExchangeProvider, IBiPoolManager, Initializable, Ownable {
  using FixidityLib for FixidityLib.Fraction;
  using SafeMath for uint256;

  /* ==================== State Variables ==================== */

  // Address of the broker contract.
  address public broker;

  // Maps an exchange id to the corresponding PoolExchange struct.
  // exchangeId is in the format "asset0Symbol:asset1Symbol:pricingModuleName"
  mapping(bytes32 => PoolExchange) public exchanges;
  bytes32[] public exchangeIds;

  // Address of the Mento reserve contract
  IReserve public reserve;

  // Address of the Mento reserve contract
  ISortedOracles public sortedOracles;

  /* ==================== Constructor ==================== */

  /**
   * @notice Sets initialized == true on implementation contracts.
   * @param test Set to true to skip implementation initialization.
   */
  // solhint-disable-next-line no-empty-blocks
  constructor(bool test) public Initializable(test) {}

  /**
   * @notice Allows the contract to be upgradable via the proxy.
   * @param _broker The address of the broker contract.
   * @param _reserve The address of the reserve contract.
   */
  function initialize(
    address _broker,
    IReserve _reserve,
    ISortedOracles _sortedOracles
  ) external initializer {
    _transferOwnership(msg.sender);
    setBroker(_broker);
    setReserve(_reserve);
    setSortedOracles(_sortedOracles);
  }

  /* ==================== Modifiers ==================== */

  modifier onlyBroker() {
    require(msg.sender == broker, "Caller is not the Broker");
    _;
  }

  /* ==================== View Functions ==================== */

  /**
   * @notice Get a PoolExchange from storage.
   * @param exchangeId the exchange id
   */
  function getPoolExchange(bytes32 exchangeId) public view returns (PoolExchange memory exchange) {
    exchange = exchanges[exchangeId];
    require(exchange.asset0 != address(0), "An exchange with the specified id does not exist");
  }

  /**
   * @notice Get all exchange IDs.
   * @return exchangeIds List of the exchangeIds.
   */
  function getExchangeIds() external view returns (bytes32[] memory) {
    return exchangeIds;
  }

  /**
   * @notice Get all exchanges (used by interfaces)
   * @dev We don't expect the number of exchanges to grow to
   * astronomical values so this is safe gas-wise as is.
   */
  function getExchanges() public view returns (Exchange[] memory _exchanges) {
    _exchanges = new Exchange[](exchangeIds.length);
    for (uint256 i = 0; i < exchangeIds.length; i++) {
      _exchanges[i].exchangeId = exchangeIds[i];
      _exchanges[i].assets = new address[](2);
      _exchanges[i].assets[0] = exchanges[exchangeIds[i]].asset0;
      _exchanges[i].assets[1] = exchanges[exchangeIds[i]].asset1;
    }
  }

  /**
   * @notice Calculate amountOut of tokenOut received for a given amountIn of tokenIn
   * @param exchangeId The id of the exchange i.e PoolExchange to use
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountIn The amount of tokenIn to be sold
   * @return amountOut The amount of tokenOut to be bought
   */
  function getAmountOut(
    bytes32 exchangeId,
    address tokenIn,
    address tokenOut,
    uint256 amountIn
  ) external view returns (uint256 amountOut) {
    PoolExchange memory exchange = getPoolExchange(exchangeId);
    (amountOut, ) = _getAmountOut(exchange, tokenIn, tokenOut, amountIn);
  }

  /**
   * @notice Calculate amountIn of tokenIn for a given amountIn of tokenIn
   * @param exchangeId The id of the exchange i.e PoolExchange to use
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountOut The amount of tokenOut to be bought
   * @return amountIn The amount of tokenIn to be sold
   */
  function getAmountIn(
    bytes32 exchangeId,
    address tokenIn,
    address tokenOut,
    uint256 amountOut
  ) external view returns (uint256 amountIn) {
    PoolExchange memory exchange = getPoolExchange(exchangeId);
    (amountIn, ) = _getAmountIn(exchange, tokenIn, tokenOut, amountOut);
  }

  /* ==================== Mutative Functions ==================== */

  /**
   * @notice Sets the address of the broker contract.
   * @param _broker The new address of the broker contract.
   */
  function setBroker(address _broker) public onlyOwner {
    require(_broker != address(0), "Broker address must be set");
    broker = _broker;
    emit BrokerUpdated(_broker);
  }

  /**
   * @notice Sets the address of the reserve contract.
   * @param _reserve The new address of the reserve contract.
   */
  function setReserve(IReserve _reserve) public onlyOwner {
    require(address(_reserve) != address(0), "Reserve address must be set");
    reserve = _reserve;
    emit ReserveUpdated(address(_reserve));
  }

  /**
   * @notice Sets the address of the sortedOracles contract.
   * @param _sortedOracles The new address of the sorted oracles contract.
   */
  function setSortedOracles(ISortedOracles _sortedOracles) public onlyOwner {
    require(address(_sortedOracles) != address(0), "SortedOracles address must be set");
    sortedOracles = _sortedOracles;
    emit SortedOraclesUpdated(address(_sortedOracles));
  }

  /**
   * @notice Creates a new exchange using the given parameters.
   * @param _exchange the PoolExchange to create.
   * @return exchangeId The id of the newly created exchange.
   */
  function createExchange(PoolExchange calldata _exchange) external onlyOwner returns (bytes32 exchangeId) {
    PoolExchange memory exchange = _exchange;
    require(address(exchange.pricingModule) != address(0), "pricingModule must be set");
    require(exchange.asset0 != address(0), "asset0 must be set");
    require(exchange.asset1 != address(0), "asset1 must be set");

    exchangeId = keccak256(
      abi.encodePacked(
        IERC20Metadata(exchange.asset0).symbol(),
        IERC20Metadata(exchange.asset1).symbol(),
        exchange.pricingModule.name()
      )
    );
    require(exchanges[exchangeId].asset0 == address(0), "An exchange with the specified assets and exchange exists");

    validate(exchange);
    (uint256 bucket0, uint256 bucket1) = getUpdatedBuckets(exchange);

    exchange.bucket0 = bucket0;
    exchange.bucket1 = bucket1;

    exchanges[exchangeId] = exchange;
    exchangeIds.push(exchangeId);

    emit ExchangeCreated(exchangeId, exchange.asset0, exchange.asset1, address(exchange.pricingModule));
  }

  /**
   * @notice Destroys a exchange with the given parameters if it exists and frees up
   *         the collateral and stable allocation it was using.
   * @param exchangeId the id of the exchange to destroy
   * @param exchangeIdIndex The index of the exchangeId in the ids array
   * @return destroyed A boolean indicating whether or not the exchange was successfully destroyed.
   */
  function destroyExchange(bytes32 exchangeId, uint256 exchangeIdIndex) external onlyOwner returns (bool destroyed) {
    require(exchangeIdIndex < exchangeIds.length, "exchangeIdIndex not in range");
    require(exchangeIds[exchangeIdIndex] == exchangeId, "exchangeId at index doesn't match");
    PoolExchange memory exchange = exchanges[exchangeId];

    delete exchanges[exchangeId];
    exchangeIds[exchangeIdIndex] = exchangeIds[exchangeIds.length - 1];
    exchangeIds.pop();
    destroyed = true;

    emit ExchangeDestroyed(exchangeId, exchange.asset0, exchange.asset1, address(exchange.pricingModule));
  }

  /**
   * @notice Execute a token swap with fixed amountIn
   * @param exchangeId The id of exchange, i.e. PoolExchange to use
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountIn The amount of tokenIn to be sold
   * @return amountOut The amount of tokenOut to be bought
   */
  function swapIn(
    bytes32 exchangeId,
    address tokenIn,
    address tokenOut,
    uint256 amountIn
  ) external onlyBroker returns (uint256 amountOut) {
    PoolExchange memory exchange = getPoolExchange(exchangeId);
    bool bucketsUpdated;

    (amountOut, bucketsUpdated) = _getAmountOut(exchange, tokenIn, tokenOut, amountIn);
    executeSwap(exchangeId, exchange, tokenIn, amountIn, amountOut, bucketsUpdated);
    return amountOut;
  }

  /**
   * @notice Execute a token swap with fixed amountOut
   * @param exchangeId The id of exchange, i.e. PoolExchange to use
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountOut The amount of tokenOut to be bought
   * @return amountIn The amount of tokenIn to be sold
   */
  function swapOut(
    bytes32 exchangeId,
    address tokenIn,
    address tokenOut,
    uint256 amountOut
  ) external onlyBroker returns (uint256 amountIn) {
    PoolExchange memory exchange = getPoolExchange(exchangeId);
    bool bucketsUpdated;

    (amountIn, bucketsUpdated) = _getAmountIn(exchange, tokenIn, tokenOut, amountOut);
    executeSwap(exchangeId, exchange, tokenIn, amountIn, amountOut, bucketsUpdated);
    return amountIn;
  }

  /* ==================== Private Functions ==================== */

  /**
   * @notice Execute a swap against the in memory exchange and write
   * the new bucket sizes to storage.
   * @param exchangeId The id of the exchange
   * @param exchange The exchange to operate on
   * @param tokenIn The token to be sold
   * @param amountIn The amount of tokenIn to be sold
   * @param amountOut The amount of tokenOut to be bought
   * @param bucketsUpdated wether the buckets updated during the swap
   */
  function executeSwap(
    bytes32 exchangeId,
    PoolExchange memory exchange,
    address tokenIn,
    uint256 amountIn,
    uint256 amountOut,
    bool bucketsUpdated
  ) internal {
    if (bucketsUpdated) {
      // solhint-disable-next-line not-rely-on-time
      exchanges[exchangeId].lastBucketUpdate = now;
      emit BucketsUpdated(exchangeId, exchange.bucket0, exchange.bucket1);
    }

    if (tokenIn == exchange.asset0) {
      exchanges[exchangeId].bucket0 = exchange.bucket0 + amountIn;
      exchanges[exchangeId].bucket1 = exchange.bucket1 - amountOut;
    } else {
      exchanges[exchangeId].bucket0 = exchange.bucket0 - amountOut;
      exchanges[exchangeId].bucket1 = exchange.bucket1 + amountIn;
    }
  }

  /**
   * @notice Calculate amountOut of tokenOut received for a given amountIn of tokenIn
   * @param exchange The exchange to operate on
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountIn The amount of tokenIn to be sold
   * @return amountOut The amount of tokenOut to be bought
   * @return bucketsUpdated Wether the buckets were updated during the quote
   */
  function _getAmountOut(
    PoolExchange memory exchange,
    address tokenIn,
    address tokenOut,
    uint256 amountIn
  ) internal view returns (uint256 amountOut, bool bucketsUpdated) {
    require(
      (tokenIn == exchange.asset0 && tokenOut == exchange.asset1) ||
        (tokenIn == exchange.asset1 && tokenOut == exchange.asset0),
      "tokenIn and tokenOut must match exchange"
    );

    (exchange, bucketsUpdated) = updateBucketsIfNecessary(exchange);

    if (tokenIn == exchange.asset0) {
      amountOut = exchange.pricingModule.getAmountOut(
        exchange.bucket0,
        exchange.bucket1,
        exchange.config.spread.unwrap(),
        amountIn
      );
    } else {
      amountOut = exchange.pricingModule.getAmountOut(
        exchange.bucket1,
        exchange.bucket0,
        exchange.config.spread.unwrap(),
        amountIn
      );
    }
  }

  /**
   * @notice Calculate amountIn of tokenIn for a given amountIn of tokenIn
   * @param exchange The exchange to operate on
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountOut The amount of tokenOut to be bought
   * @return amountIn The amount of tokenIn to be sold
   * @return bucketsUpdated Wether the buckets were updated during the quote
   */
  function _getAmountIn(
    PoolExchange memory exchange,
    address tokenIn,
    address tokenOut,
    uint256 amountOut
  ) internal view returns (uint256 amountIn, bool bucketsUpdated) {
    require(
      (tokenIn == exchange.asset0 && tokenOut == exchange.asset1) ||
        (tokenIn == exchange.asset1 && tokenOut == exchange.asset0),
      "tokenIn and tokenOut must match exchange"
    );

    (exchange, bucketsUpdated) = updateBucketsIfNecessary(exchange);

    if (tokenIn == exchange.asset0) {
      amountIn = exchange.pricingModule.getAmountIn(
        exchange.bucket0,
        exchange.bucket1,
        exchange.config.spread.unwrap(),
        amountOut
      );
    } else {
      amountIn = exchange.pricingModule.getAmountIn(
        exchange.bucket1,
        exchange.bucket0,
        exchange.config.spread.unwrap(),
        amountOut
      );
    }
  }

  /**
   * @notice If conditions are met, update the exchange bucket sizes.
   * @dev This doesn't checkpoint the exchange, just updates the in-memory one
   * so it should be used in a context that then checkpoints the exchange.
   * @param exchange The exchange being updated.
   * @return exchangeAfter The updated exchange.
   */
  function updateBucketsIfNecessary(PoolExchange memory exchange)
    internal
    view
    returns (PoolExchange memory, bool updated)
  {
    if (shouldUpdateBuckets(exchange)) {
      (exchange.bucket0, exchange.bucket1) = getUpdatedBuckets(exchange);
      updated = true;
    }
    return (exchange, updated);
  }

  /**
   * @notice Determine if a exchange's buckets should be updated
   * based on staleness of buckets and oracle rates.
   * @param exchange The PoolExchange.
   * @return shouldUpdate
   */
  function shouldUpdateBuckets(PoolExchange memory exchange) internal view returns (bool) {
    (bool isReportExpired, ) = sortedOracles.isOldestReportExpired(exchange.config.oracleReportTarget);
    // solhint-disable-next-line not-rely-on-time
    bool timePassed = now >= exchange.lastBucketUpdate.add(exchange.config.referenceRateResetFrequency);
    bool enoughReports = (sortedOracles.numRates(exchange.config.oracleReportTarget) >= exchange.config.minimumReports);
    // solhint-disable-next-line not-rely-on-time
    bool medianReportRecent = sortedOracles.medianTimestamp(exchange.config.oracleReportTarget) >
      now.sub(exchange.config.referenceRateResetFrequency);
    return timePassed && enoughReports && medianReportRecent && !isReportExpired;
  }

  /**
   * @notice Calculate the new bucket sizes for a exchange.
   * @param exchange The PoolExchange in context.
   * @return bucket0 The size of bucket0.
   * @return bucket1 The size of bucket1.
   */
  function getUpdatedBuckets(PoolExchange memory exchange) internal view returns (uint256 bucket0, uint256 bucket1) {
    // TODO: Take max fraction/min supply in account when setting the bucket size
    bucket0 = exchange.config.stablePoolResetSize;
    uint256 exchangeRateNumerator;
    uint256 exchangeRateDenominator;
    (exchangeRateNumerator, exchangeRateDenominator) = getOracleExchangeRate(exchange.config.oracleReportTarget);

    bucket1 = exchangeRateDenominator.mul(bucket0).div(exchangeRateNumerator);
  }

  /**
   * @notice Get the exchange rate as numerator,denominator from sorted oracles
   * and protect in case of a 0-denominator.
   * @param target the reportTarget to read from SortedOracles
   * @return rateNumerator
   * @return rateDenominator
   */
  function getOracleExchangeRate(address target) internal view returns (uint256, uint256) {
    uint256 rateNumerator;
    uint256 rateDenominator;
    (rateNumerator, rateDenominator) = sortedOracles.medianRate(target);
    require(rateDenominator > 0, "exchange rate denominator must be greater than 0");
    return (rateNumerator, rateDenominator);
  }

  /**
   * @notice Valitates a PoolExchange's parameters and configuration
   * @dev Reverts if not valid
   * @param exchange The PoolExchange to validate
   */
  function validate(PoolExchange memory exchange) private view {
    require(reserve.isStableAsset(exchange.asset0), "asset0 must be a stable registered with the reserve");
    require(
      reserve.isStableAsset(exchange.asset1) || reserve.isCollateralAsset(exchange.asset1),
      "asset1 must be a stable or collateral"
    );

    require(FixidityLib.lte(exchange.config.spread, FixidityLib.fixed1()), "spread must be less than or equal to 1");

    require(exchange.config.oracleReportTarget != address(0), "oracleReportTarget must be set");

    // TODO: Stable bucket max fraction should not exceed available stable bucket fraction.
    // TODO: minSupplyForStableBucketCap gt 0 & is there an aggregated value that needs to be checked
  }
}
        

pragma solidity ^0.5.13;

interface IFreezer {
  function isFrozen(address) external view returns (bool);
}
          

pragma solidity ^0.5.13;

interface ICeloVersionedContract {
  /**
   * @notice Returns the storage, major, minor, and patch version of the contract.
   * @return Storage version of the contract.
   * @return Major version of the contract.
   * @return Minor version of the contract.
   * @return Patch version of the contract.
   */
  function getVersionNumber()
    external
    pure
    returns (
      uint256,
      uint256,
      uint256,
      uint256
    );
}
          

pragma solidity ^0.5.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: 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
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}
          

pragma solidity ^0.5.0;

import "../GSN/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Returns true if the caller is the current owner.
     */
    function isOwner() public view returns (bool) {
        return _msgSender() == _owner;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}
          

pragma solidity ^0.5.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}
          

pragma solidity ^0.5.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }
    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}
          

pragma solidity ^0.5.13;

/**
 * @title This interface describes the functions specific to Celo Stable Tokens, and in the
 * absence of interface inheritance is intended as a companion to IERC20.sol and ICeloToken.sol.
 */
interface IStableToken {
  function mint(address, uint256) external returns (bool);

  function burn(uint256) external returns (bool);

  function setInflationParameters(uint256, uint256) external;

  function valueToUnits(uint256) external view returns (uint256);

  function unitsToValue(uint256) external view returns (uint256);

  function getInflationParameters()
    external
    view
    returns (
      uint256,
      uint256,
      uint256,
      uint256
    );

  // NOTE: duplicated with IERC20.sol, remove once interface inheritance is supported.
  function balanceOf(address) external view returns (uint256);
}
          

pragma solidity ^0.5.13;

interface ISortedOracles {
  function addOracle(address, address) external;

  function removeOracle(
    address,
    address,
    uint256
  ) external;

  function report(
    address,
    uint256,
    address,
    address
  ) external;

  function removeExpiredReports(address, uint256) external;

  function isOldestReportExpired(address token) external view returns (bool, address);

  function numRates(address) external view returns (uint256);

  function medianRate(address) external view returns (uint256, uint256);

  function numTimestamps(address) external view returns (uint256);

  function medianTimestamp(address) external view returns (uint256);
}
          

pragma solidity ^0.5.13;

interface IReserve {
  function setTobinTaxStalenessThreshold(uint256) external;

  function addToken(address) external returns (bool);

  function removeToken(address, uint256) external returns (bool);

  function transferGold(address payable, uint256) external returns (bool);

  function transferExchangeGold(address payable, uint256) external returns (bool);

  function transferCollateralAsset(
    address collateralAsset,
    address payable to,
    uint256 value
  ) external returns (bool);

  function getReserveGoldBalance() external view returns (uint256);

  function getUnfrozenReserveGoldBalance() external view returns (uint256);

  function getOrComputeTobinTax() external returns (uint256, uint256);

  function getTokens() external view returns (address[] memory);

  function getReserveRatio() external view returns (uint256);

  function addExchangeSpender(address) external;

  function removeExchangeSpender(address, uint256) external;

  function addSpender(address) external;

  function removeSpender(address) external;

  function isStableAsset(address) external view returns (bool);

  function isCollateralAsset(address) external view returns (bool);

  function getDailySpendingRatioForCollateralAsset(address collateralAsset) external view returns (uint256);
}
          

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity ^0.5.13;

/**
 * @title Interface for a Mento Pricing Module.
 * @notice A Mento pricing module represents an exchange relation between a pair of ERC20 assets.
 */
interface IPricingModule {
  /**
   * @notice Returns the output amount and new bucket sizes for a given input amount.
   * @param tokenInBucketSize Size of the tokenIn bucket.
   * @param tokenOutBucketSize Size of the tokenOut bucket.
   * @param spread Spread charged on exchanges.
   * @param amountIn Amount of tokenIn being paid in.
   * @return amountOut Amount of tokenOut that will be paid out.
   */
  function getAmountOut(
    uint256 tokenInBucketSize,
    uint256 tokenOutBucketSize,
    uint256 spread,
    uint256 amountIn
  ) external view returns (uint256 amountOut);

  /**
   * @notice Returns the input amount necessary for a given output amount.
   * @param tokenInBucketSize Size of the tokenIn bucket.
   * @param tokenOutBucketSize Size of the tokenOut bucket.
   * @param spread Spread charged on exchanges.
   * @param amountOut Amount of tokenIn being paid out.
   * @return amountIn Amount of tokenOut that would have to be paid in.
   */
  function getAmountIn(
    uint256 tokenInBucketSize,
    uint256 tokenOutBucketSize,
    uint256 spread,
    uint256 amountOut
  ) external view returns (uint256 amountIn);

  /**
   * @notice Retrieve the name of this pricing module.
   * @return exchangeName The name of the pricing module.
   */
  function name() external view returns (string memory pricingModuleName);
}
          

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity ^0.5.13;
pragma experimental ABIEncoderV2;

/**
 * @title ExchangeProvider interface
 * @notice The IExchangeProvider interface is the interface that the Broker uses
 * to communicate with different exchange manager implementations like the BiPoolManager
 */
interface IExchangeProvider {
  /**
   * @notice Exchange - a struct that's used only by UIs (frontends/CLIs)
   * in order to discover what asset swaps are possible within an
   * exchange provider.
   * It's up to the specific exchange provider to convert its internal
   * representation to this universal struct. This conversion should
   * only happen in view calls used for discovery.
   * @param exchangeId The ID of the exchange, used to initiate swaps or get quotes.
   * @param assets An array of addresses of ERC20 tokens that can be swapped.
   */
  struct Exchange {
    bytes32 exchangeId;
    address[] assets;
  }

  /**
   * @notice Get all exchanges supported by the ExchangeProvider.
   * @return exchanges An array of Exchange structs.
   */
  function getExchanges() external view returns (Exchange[] memory exchanges);

  /**
   * @notice Execute a token swap with fixed amountIn
   * @param exchangeId The id of the exchange to use
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountIn The amount of tokenIn to be sold
   * @return amountOut The amount of tokenOut to be bought
   */
  function swapIn(
    bytes32 exchangeId,
    address tokenIn,
    address tokenOut,
    uint256 amountIn
  ) external returns (uint256 amountOut);

  /**
   * @notice Execute a token swap with fixed amountOut
   * @param exchangeId The id of the exchange to use
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountOut The amount of tokenOut to be bought
   * @return amountIn The amount of tokenIn to be sold
   */
  function swapOut(
    bytes32 exchangeId,
    address tokenIn,
    address tokenOut,
    uint256 amountOut
  ) external returns (uint256 amountIn);

  /**
   * @notice Calculate amountOut of tokenOut received for a given amountIn of tokenIn
   * @param exchangeId The id of the exchange to use
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountIn The amount of tokenIn to be sold
   * @return amountOut The amount of tokenOut to be bought
   */
  function getAmountOut(
    bytes32 exchangeId,
    address tokenIn,
    address tokenOut,
    uint256 amountIn
  ) external view returns (uint256 amountOut);

  /**
   * @notice Calculate amountIn of tokenIn needed for a given amountOut of tokenOut
   * @param exchangeId The id of the exchange to use
   * @param tokenIn The token to be sold
   * @param tokenOut The token to be bought
   * @param amountOut The amount of tokenOut to be bought
   * @return amountIn The amount of tokenIn to be sold
   */
  function getAmountIn(
    bytes32 exchangeId,
    address tokenIn,
    address tokenOut,
    uint256 amountOut
  ) external view returns (uint256 amountIn);
}
          

pragma solidity ^0.5.13;

interface IExchange {
  function buy(
    uint256,
    uint256,
    bool
  ) external returns (uint256);

  function sell(
    uint256,
    uint256,
    bool
  ) external returns (uint256);

  function exchange(
    uint256,
    uint256,
    bool
  ) external returns (uint256);

  function setUpdateFrequency(uint256) external;

  function getBuyTokenAmount(uint256, bool) external view returns (uint256);

  function getSellTokenAmount(uint256, bool) external view returns (uint256);

  function getBuyAndSellBuckets(bool) external view returns (uint256, uint256);
}
          

pragma solidity ^0.5.13;

/**
 * @title This interface describes the non- ERC20 shared interface for all Celo Tokens, and
 * in the absence of interface inheritance is intended as a companion to IERC20.sol.
 */
interface ICeloToken {
  function transferWithComment(
    address,
    uint256,
    string calldata
  ) external returns (bool);

  function name() external view returns (string memory);

  function symbol() external view returns (string memory);

  function decimals() external view returns (uint8);
}
          

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity ^0.5.13;
pragma experimental ABIEncoderV2;

import { IPricingModule } from "./IPricingModule.sol";
import { FixidityLib } from "../common/FixidityLib.sol";

/**
 * @title BiPool Manager interface
 * @notice The two asset pool manager is responsible for
 * managing the state of all two-asset virtual pools.
 */
interface IBiPoolManager {
  /**
   * @title PoolExchange
   * @notice The PoolExchange is a type of asset exchange that
   * that implements an AMM with two virtual buckets.
   */
  struct PoolExchange {
    address asset0;
    address asset1;
    IPricingModule pricingModule;
    uint256 bucket0;
    uint256 bucket1;
    uint256 lastBucketUpdate;
    PoolConfig config;
  }

  /**
   * @notice Variables related to bucket updates and sizing.
   * @dev Broken down into a separate struct because the compiler
   * version doesn't support structs with too many members.
   * Sad reacts only.
   */
  struct PoolConfig {
    FixidityLib.Fraction spread;
    address oracleReportTarget; // can be a stable address or custom
    uint256 referenceRateResetFrequency;
    uint256 minimumReports;
    uint256 stablePoolResetSize;
  }

  /**
   * @notice Emitted when a new PoolExchange has been created.
   * @param exchangeId The id of the new PoolExchange
   * @param asset0 The address of asset0
   * @param asset1 The address of asset1
   * @param pricingModule the address of the pricingModule
   */
  event ExchangeCreated(
    bytes32 indexed exchangeId,
    address indexed asset0,
    address indexed asset1,
    address pricingModule
  );

  /**
   * @notice Emitted when a PoolExchange has been destroyed.
   * @param exchangeId The id of the PoolExchange
   * @param asset0 The address of asset0
   * @param asset1 The address of asset1
   * @param pricingModule the address of the pricingModule
   */
  event ExchangeDestroyed(
    bytes32 indexed exchangeId,
    address indexed asset0,
    address indexed asset1,
    address pricingModule
  );

  /**
   * @notice Emitted when the broker address is updated.
   * @param newBroker The address of the new broker.
   */
  event BrokerUpdated(address indexed newBroker);

  /**
   * @notice Emitted when the reserve address is updated.
   * @param newReserve The address of the new reserve.
   */
  event ReserveUpdated(address indexed newReserve);

  /**
   * @notice Emitted when the sortedOracles address is updated.
   * @param newSortedOracles The address of the new sortedOracles.
   */
  event SortedOraclesUpdated(address indexed newSortedOracles);

  /**
   * @notice Emitted when the buckets for a specified exchange are updated.
   * @param exchangeId The id of the exchange
   * @param bucket0 The new bucket0 size
   * @param bucket1 The new bucket1 size
   */
  event BucketsUpdated(bytes32 indexed exchangeId, uint256 bucket0, uint256 bucket1);

  /**
   * @notice Retrieves the pool with the specified exchangeId.
   * @param exchangeId The id of the pool to be retrieved.
   * @return exchange The PoolExchange with that ID.
   */
  function getPoolExchange(bytes32 exchangeId) external view returns (PoolExchange memory exchange);

  /**
   * @notice Get all exchange IDs.
   * @return exchangeIds List of the exchangeIds.
   */
  function getExchangeIds() external view returns (bytes32[] memory exchangeIds);

  /**
   * @notice Create a PoolExchange with the provided data.
   * @param exchange The PoolExchange to be created.
   * @return exchangeId The id of the exchange.
   */
  function createExchange(PoolExchange calldata exchange) external returns (bytes32 exchangeId);

  /**
   * @notice Delete a PoolExchange.
   * @param exchangeId The PoolExchange to be created.
   * @param exchangeIdIndex The index of the exchangeId in the exchangeIds array.
   * @return destroyed - true on successful delition.
   */
  function destroyExchange(bytes32 exchangeId, uint256 exchangeIdIndex) external returns (bool destroyed);
}
          

pragma solidity ^0.5.13;

interface IRegistry {
  function setAddressFor(string calldata, address) external;

  function getAddressForOrDie(bytes32) external view returns (address);

  function getAddressFor(bytes32) external view returns (address);

  function getAddressForStringOrDie(string calldata identifier) external view returns (address);

  function getAddressForString(string calldata identifier) external view returns (address);

  function isOneOf(bytes32[] calldata, address) external view returns (bool);
}
          

pragma solidity ^0.5.13;

import "openzeppelin-solidity/contracts/ownership/Ownable.sol";
import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";

import "./interfaces/IFreezer.sol";
import "./interfaces/IRegistry.sol";

import "../interfaces/IExchange.sol";
import "../interfaces/IReserve.sol";
import "../interfaces/ISortedOracles.sol";
import "../interfaces/IStableToken.sol";

contract UsingRegistry is Ownable {
  event RegistrySet(address indexed registryAddress);

  // solhint-disable state-visibility
  bytes32 constant ACCOUNTS_REGISTRY_ID = keccak256(abi.encodePacked("Accounts"));
  bytes32 constant ATTESTATIONS_REGISTRY_ID = keccak256(abi.encodePacked("Attestations"));
  bytes32 constant DOWNTIME_SLASHER_REGISTRY_ID = keccak256(abi.encodePacked("DowntimeSlasher"));
  bytes32 constant DOUBLE_SIGNING_SLASHER_REGISTRY_ID = keccak256(abi.encodePacked("DoubleSigningSlasher"));
  bytes32 constant ELECTION_REGISTRY_ID = keccak256(abi.encodePacked("Election"));
  bytes32 constant EXCHANGE_REGISTRY_ID = keccak256(abi.encodePacked("Exchange"));
  bytes32 constant FEE_CURRENCY_WHITELIST_REGISTRY_ID = keccak256(abi.encodePacked("FeeCurrencyWhitelist"));
  bytes32 constant FREEZER_REGISTRY_ID = keccak256(abi.encodePacked("Freezer"));
  bytes32 constant GOLD_TOKEN_REGISTRY_ID = keccak256(abi.encodePacked("GoldToken"));
  bytes32 constant GOVERNANCE_REGISTRY_ID = keccak256(abi.encodePacked("Governance"));
  bytes32 constant GOVERNANCE_SLASHER_REGISTRY_ID = keccak256(abi.encodePacked("GovernanceSlasher"));
  bytes32 constant LOCKED_GOLD_REGISTRY_ID = keccak256(abi.encodePacked("LockedGold"));
  bytes32 constant RESERVE_REGISTRY_ID = keccak256(abi.encodePacked("Reserve"));
  bytes32 constant RANDOM_REGISTRY_ID = keccak256(abi.encodePacked("Random"));
  bytes32 constant SORTED_ORACLES_REGISTRY_ID = keccak256(abi.encodePacked("SortedOracles"));
  bytes32 constant STABLE_TOKEN_REGISTRY_ID = keccak256(abi.encodePacked("StableToken"));
  bytes32 constant VALIDATORS_REGISTRY_ID = keccak256(abi.encodePacked("Validators"));
  // solhint-enable state-visibility

  IRegistry public registry;

  modifier onlyRegisteredContract(bytes32 identifierHash) {
    require(registry.getAddressForOrDie(identifierHash) == msg.sender, "only registered contract");
    _;
  }

  modifier onlyRegisteredContracts(bytes32[] memory identifierHashes) {
    require(registry.isOneOf(identifierHashes, msg.sender), "only registered contracts");
    _;
  }

  /**
   * @notice Updates the address pointing to a Registry contract.
   * @param registryAddress The address of a registry contract for routing to other contracts.
   */
  function setRegistry(address registryAddress) public onlyOwner {
    require(registryAddress != address(0), "Cannot register the null address");
    registry = IRegistry(registryAddress);
    emit RegistrySet(registryAddress);
  }

  function getExchange() internal view returns (IExchange) {
    return IExchange(registry.getAddressForOrDie(EXCHANGE_REGISTRY_ID));
  }

  function getFreezer() internal view returns (IFreezer) {
    return IFreezer(registry.getAddressForOrDie(FREEZER_REGISTRY_ID));
  }

  function getGoldToken() internal view returns (IERC20) {
    return IERC20(registry.getAddressForOrDie(GOLD_TOKEN_REGISTRY_ID));
  }

  function getReserve() internal view returns (IReserve) {
    return IReserve(registry.getAddressForOrDie(RESERVE_REGISTRY_ID));
  }

  function getSortedOracles() internal view returns (ISortedOracles) {
    return ISortedOracles(registry.getAddressForOrDie(SORTED_ORACLES_REGISTRY_ID));
  }

  function getStableToken() internal view returns (IStableToken) {
    return IStableToken(registry.getAddressForOrDie(STABLE_TOKEN_REGISTRY_ID));
  }
}
          

// solhint-disable state-visibility
pragma solidity ^0.5.13;

import "openzeppelin-solidity/contracts/math/SafeMath.sol";
import "./interfaces/ICeloVersionedContract.sol";

contract UsingPrecompiles {
  using SafeMath for uint256;

  address constant TRANSFER = address(0xff - 2);
  address constant FRACTION_MUL = address(0xff - 3);
  address constant PROOF_OF_POSSESSION = address(0xff - 4);
  address constant GET_VALIDATOR = address(0xff - 5);
  address constant NUMBER_VALIDATORS = address(0xff - 6);
  address constant EPOCH_SIZE = address(0xff - 7);
  address constant BLOCK_NUMBER_FROM_HEADER = address(0xff - 8);
  address constant HASH_HEADER = address(0xff - 9);
  address constant GET_PARENT_SEAL_BITMAP = address(0xff - 10);
  address constant GET_VERIFIED_SEAL_BITMAP = address(0xff - 11);

  /**
   * @notice calculate a * b^x for fractions a, b to `decimals` precision
   * @param aNumerator Numerator of first fraction
   * @param aDenominator Denominator of first fraction
   * @param bNumerator Numerator of exponentiated fraction
   * @param bDenominator Denominator of exponentiated fraction
   * @param exponent exponent to raise b to
   * @param _decimals precision
   * @return Numerator of the computed quantity (not reduced).
   * @return Denominator of the computed quantity (not reduced).
   */
  function fractionMulExp(
    uint256 aNumerator,
    uint256 aDenominator,
    uint256 bNumerator,
    uint256 bDenominator,
    uint256 exponent,
    uint256 _decimals
  ) public view returns (uint256, uint256) {
    require(aDenominator != 0 && bDenominator != 0, "a denominator is zero");
    uint256 returnNumerator;
    uint256 returnDenominator;
    bool success;
    bytes memory out;
    (success, out) = FRACTION_MUL.staticcall(
      abi.encodePacked(aNumerator, aDenominator, bNumerator, bDenominator, exponent, _decimals)
    );
    require(success, "error calling fractionMulExp precompile");
    returnNumerator = getUint256FromBytes(out, 0);
    returnDenominator = getUint256FromBytes(out, 32);
    return (returnNumerator, returnDenominator);
  }

  /**
   * @notice Returns the current epoch size in blocks.
   * @return The current epoch size in blocks.
   */
  function getEpochSize() public view returns (uint256) {
    bytes memory out;
    bool success;
    (success, out) = EPOCH_SIZE.staticcall(abi.encodePacked());
    require(success, "error calling getEpochSize precompile");
    return getUint256FromBytes(out, 0);
  }

  /**
   * @notice Returns the epoch number at a block.
   * @param blockNumber Block number where epoch number is calculated.
   * @return Epoch number.
   */
  function getEpochNumberOfBlock(uint256 blockNumber) public view returns (uint256) {
    return epochNumberOfBlock(blockNumber, getEpochSize());
  }

  /**
   * @notice Returns the epoch number at a block.
   * @return Current epoch number.
   */
  function getEpochNumber() public view returns (uint256) {
    return getEpochNumberOfBlock(block.number);
  }

  /**
   * @notice Returns the epoch number at a block.
   * @param blockNumber Block number where epoch number is calculated.
   * @param epochSize The epoch size in blocks.
   * @return Epoch number.
   */
  function epochNumberOfBlock(uint256 blockNumber, uint256 epochSize) internal pure returns (uint256) {
    // Follows GetEpochNumber from celo-blockchain/blob/master/consensus/istanbul/utils.go
    uint256 epochNumber = blockNumber / epochSize;
    if (blockNumber % epochSize == 0) {
      return epochNumber;
    } else {
      return epochNumber.add(1);
    }
  }

  /**
   * @notice Gets a validator address from the current validator set.
   * @param index Index of requested validator in the validator set.
   * @return Address of validator at the requested index.
   */
  function validatorSignerAddressFromCurrentSet(uint256 index) public view returns (address) {
    bytes memory out;
    bool success;
    (success, out) = GET_VALIDATOR.staticcall(abi.encodePacked(index, uint256(block.number)));
    require(success, "error calling validatorSignerAddressFromCurrentSet precompile");
    return address(getUint256FromBytes(out, 0));
  }

  /**
   * @notice Gets a validator address from the validator set at the given block number.
   * @param index Index of requested validator in the validator set.
   * @param blockNumber Block number to retrieve the validator set from.
   * @return Address of validator at the requested index.
   */
  function validatorSignerAddressFromSet(uint256 index, uint256 blockNumber) public view returns (address) {
    bytes memory out;
    bool success;
    (success, out) = GET_VALIDATOR.staticcall(abi.encodePacked(index, blockNumber));
    require(success, "error calling validatorSignerAddressFromSet precompile");
    return address(getUint256FromBytes(out, 0));
  }

  /**
   * @notice Gets the size of the current elected validator set.
   * @return Size of the current elected validator set.
   */
  function numberValidatorsInCurrentSet() public view returns (uint256) {
    bytes memory out;
    bool success;
    (success, out) = NUMBER_VALIDATORS.staticcall(abi.encodePacked(uint256(block.number)));
    require(success, "error calling numberValidatorsInCurrentSet precompile");
    return getUint256FromBytes(out, 0);
  }

  /**
   * @notice Gets the size of the validator set that must sign the given block number.
   * @param blockNumber Block number to retrieve the validator set from.
   * @return Size of the validator set.
   */
  function numberValidatorsInSet(uint256 blockNumber) public view returns (uint256) {
    bytes memory out;
    bool success;
    (success, out) = NUMBER_VALIDATORS.staticcall(abi.encodePacked(blockNumber));
    require(success, "error calling numberValidatorsInSet precompile");
    return getUint256FromBytes(out, 0);
  }

  /**
   * @notice Checks a BLS proof of possession.
   * @param sender The address signed by the BLS key to generate the proof of possession.
   * @param blsKey The BLS public key that the validator is using for consensus, should pass proof
   *   of possession. 48 bytes.
   * @param blsPop The BLS public key proof-of-possession, which consists of a signature on the
   *   account address. 96 bytes.
   * @return True upon success.
   */
  function checkProofOfPossession(
    address sender,
    bytes memory blsKey,
    bytes memory blsPop
  ) public view returns (bool) {
    bool success;
    (success, ) = PROOF_OF_POSSESSION.staticcall(abi.encodePacked(sender, blsKey, blsPop));
    return success;
  }

  /**
   * @notice Parses block number out of header.
   * @param header RLP encoded header
   * @return Block number.
   */
  function getBlockNumberFromHeader(bytes memory header) public view returns (uint256) {
    bytes memory out;
    bool success;
    (success, out) = BLOCK_NUMBER_FROM_HEADER.staticcall(abi.encodePacked(header));
    require(success, "error calling getBlockNumberFromHeader precompile");
    return getUint256FromBytes(out, 0);
  }

  /**
   * @notice Computes hash of header.
   * @param header RLP encoded header
   * @return Header hash.
   */
  function hashHeader(bytes memory header) public view returns (bytes32) {
    bytes memory out;
    bool success;
    (success, out) = HASH_HEADER.staticcall(abi.encodePacked(header));
    require(success, "error calling hashHeader precompile");
    return getBytes32FromBytes(out, 0);
  }

  /**
   * @notice Gets the parent seal bitmap from the header at the given block number.
   * @param blockNumber Block number to retrieve. Must be within 4 epochs of the current number.
   * @return Bitmap parent seal with set bits at indices corresponding to signing validators.
   */
  function getParentSealBitmap(uint256 blockNumber) public view returns (bytes32) {
    bytes memory out;
    bool success;
    (success, out) = GET_PARENT_SEAL_BITMAP.staticcall(abi.encodePacked(blockNumber));
    require(success, "error calling getParentSealBitmap precompile");
    return getBytes32FromBytes(out, 0);
  }

  /**
   * @notice Verifies the BLS signature on the header and returns the seal bitmap.
   * The validator set used for verification is retrieved based on the parent hash field of the
   * header.  If the parent hash is not in the blockchain, verification fails.
   * @param header RLP encoded header
   * @return Bitmap parent seal with set bits at indices correspoinding to signing validators.
   */
  function getVerifiedSealBitmapFromHeader(bytes memory header) public view returns (bytes32) {
    bytes memory out;
    bool success;
    (success, out) = GET_VERIFIED_SEAL_BITMAP.staticcall(abi.encodePacked(header));
    require(success, "error calling getVerifiedSealBitmapFromHeader precompile");
    return getBytes32FromBytes(out, 0);
  }

  /**
   * @notice Converts bytes to uint256.
   * @param bs byte[] data
   * @param start offset into byte data to convert
   * @return uint256 data
   */
  function getUint256FromBytes(bytes memory bs, uint256 start) internal pure returns (uint256) {
    return uint256(getBytes32FromBytes(bs, start));
  }

  /**
   * @notice Converts bytes to bytes32.
   * @param bs byte[] data
   * @param start offset into byte data to convert
   * @return bytes32 data
   */
  function getBytes32FromBytes(bytes memory bs, uint256 start) internal pure returns (bytes32) {
    require(bs.length >= start.add(32), "slicing out of range");
    bytes32 x;
    // solhint-disable-next-line no-inline-assembly
    assembly {
      x := mload(add(bs, add(start, 32)))
    }
    return x;
  }

  /**
   * @notice Returns the minimum number of required signers for a given block number.
   * @dev Computed in celo-blockchain as int(math.Ceil(float64(2*valSet.Size()) / 3))
   */
  function minQuorumSize(uint256 blockNumber) public view returns (uint256) {
    return numberValidatorsInSet(blockNumber).mul(2).add(2).div(3);
  }

  /**
   * @notice Computes byzantine quorum from current validator set size
   * @return Byzantine quorum of validators.
   */
  function minQuorumSizeInCurrentSet() public view returns (uint256) {
    return minQuorumSize(block.number);
  }
}
          

pragma solidity ^0.5.13;

contract Initializable {
  bool public initialized;

  constructor(bool testingDeployment) public {
    if (!testingDeployment) {
      initialized = true;
    }
  }

  modifier initializer() {
    require(!initialized, "contract already initialized");
    initialized = true;
    _;
  }
}
          

pragma solidity ^0.5.13;

import "./UsingRegistry.sol";

contract Freezable is UsingRegistry {
  // onlyWhenNotFrozen functions can only be called when `frozen` is false, otherwise they will
  // revert.
  modifier onlyWhenNotFrozen() {
    require(!getFreezer().isFrozen(address(this)), "can't call when contract is frozen");
    _;
  }
}
          

pragma solidity ^0.5.13;

/**
 * @title FixidityLib
 * @author Gadi Guy, Alberto Cuesta Canada
 * @notice This library provides fixed point arithmetic with protection against
 * overflow.
 * All operations are done with uint256 and the operands must have been created
 * with any of the newFrom* functions, which shift the comma digits() to the
 * right and check for limits, or with wrap() which expects a number already
 * in the internal representation of a fraction.
 * When using this library be sure to use maxNewFixed() as the upper limit for
 * creation of fixed point numbers.
 * @dev All contained functions are pure and thus marked internal to be inlined
 * on consuming contracts at compile time for gas efficiency.
 */
library FixidityLib {
  struct Fraction {
    uint256 value;
  }

  /**
   * @notice Number of positions that the comma is shifted to the right.
   */
  function digits() internal pure returns (uint8) {
    return 24;
  }

  uint256 private constant FIXED1_UINT = 1000000000000000000000000;

  /**
   * @notice This is 1 in the fixed point units used in this library.
   * @dev Test fixed1() equals 10^digits()
   * Hardcoded to 24 digits.
   */
  function fixed1() internal pure returns (Fraction memory) {
    return Fraction(FIXED1_UINT);
  }

  /**
   * @notice Wrap a uint256 that represents a 24-decimal fraction in a Fraction
   * struct.
   * @param x Number that already represents a 24-decimal fraction.
   * @return A Fraction struct with contents x.
   */
  function wrap(uint256 x) internal pure returns (Fraction memory) {
    return Fraction(x);
  }

  /**
   * @notice Unwraps the uint256 inside of a Fraction struct.
   */
  function unwrap(Fraction memory x) internal pure returns (uint256) {
    return x.value;
  }

  /**
   * @notice The amount of decimals lost on each multiplication operand.
   * @dev Test mulPrecision() equals sqrt(fixed1)
   */
  function mulPrecision() internal pure returns (uint256) {
    return 1000000000000;
  }

  /**
   * @notice Maximum value that can be converted to fixed point. Optimize for deployment.
   * @dev
   * Test maxNewFixed() equals maxUint256() / fixed1()
   */
  function maxNewFixed() internal pure returns (uint256) {
    return 115792089237316195423570985008687907853269984665640564;
  }

  /**
   * @notice Converts a uint256 to fixed point Fraction
   * @dev Test newFixed(0) returns 0
   * Test newFixed(1) returns fixed1()
   * Test newFixed(maxNewFixed()) returns maxNewFixed() * fixed1()
   * Test newFixed(maxNewFixed()+1) fails
   */
  function newFixed(uint256 x) internal pure returns (Fraction memory) {
    require(x <= maxNewFixed(), "can't create fixidity number larger than maxNewFixed()");
    return Fraction(x * FIXED1_UINT);
  }

  /**
   * @notice Converts a uint256 in the fixed point representation of this
   * library to a non decimal. All decimal digits will be truncated.
   */
  function fromFixed(Fraction memory x) internal pure returns (uint256) {
    return x.value / FIXED1_UINT;
  }

  /**
   * @notice Converts two uint256 representing a fraction to fixed point units,
   * equivalent to multiplying dividend and divisor by 10^digits().
   * @param numerator numerator must be <= maxNewFixed()
   * @param denominator denominator must be <= maxNewFixed() and denominator can't be 0
   * @dev
   * Test newFixedFraction(1,0) fails
   * Test newFixedFraction(0,1) returns 0
   * Test newFixedFraction(1,1) returns fixed1()
   * Test newFixedFraction(1,fixed1()) returns 1
   */
  function newFixedFraction(uint256 numerator, uint256 denominator) internal pure returns (Fraction memory) {
    Fraction memory convertedNumerator = newFixed(numerator);
    Fraction memory convertedDenominator = newFixed(denominator);
    return divide(convertedNumerator, convertedDenominator);
  }

  /**
   * @notice Returns the integer part of a fixed point number.
   * @dev
   * Test integer(0) returns 0
   * Test integer(fixed1()) returns fixed1()
   * Test integer(newFixed(maxNewFixed())) returns maxNewFixed()*fixed1()
   */
  function integer(Fraction memory x) internal pure returns (Fraction memory) {
    return Fraction((x.value / FIXED1_UINT) * FIXED1_UINT); // Can't overflow
  }

  /**
   * @notice Returns the fractional part of a fixed point number.
   * In the case of a negative number the fractional is also negative.
   * @dev
   * Test fractional(0) returns 0
   * Test fractional(fixed1()) returns 0
   * Test fractional(fixed1()-1) returns 10^24-1
   */
  function fractional(Fraction memory x) internal pure returns (Fraction memory) {
    return Fraction(x.value - (x.value / FIXED1_UINT) * FIXED1_UINT); // Can't overflow
  }

  /**
   * @notice x+y.
   * @dev The maximum value that can be safely used as an addition operator is defined as
   * maxFixedAdd = maxUint256()-1 / 2, or
   * 57896044618658097711785492504343953926634992332820282019728792003956564819967.
   * Test add(maxFixedAdd,maxFixedAdd) equals maxFixedAdd + maxFixedAdd
   * Test add(maxFixedAdd+1,maxFixedAdd+1) throws
   */
  function add(Fraction memory x, Fraction memory y) internal pure returns (Fraction memory) {
    uint256 z = x.value + y.value;
    require(z >= x.value, "add overflow detected");
    return Fraction(z);
  }

  /**
   * @notice x-y.
   * @dev
   * Test subtract(6, 10) fails
   */
  function subtract(Fraction memory x, Fraction memory y) internal pure returns (Fraction memory) {
    require(x.value >= y.value, "substraction underflow detected");
    return Fraction(x.value - y.value);
  }

  /**
   * @notice x*y. If any of the operators is higher than the max multiplier value it
   * might overflow.
   * @dev The maximum value that can be safely used as a multiplication operator
   * (maxFixedMul) is calculated as sqrt(maxUint256()*fixed1()),
   * or 340282366920938463463374607431768211455999999999999
   * Test multiply(0,0) returns 0
   * Test multiply(maxFixedMul,0) returns 0
   * Test multiply(0,maxFixedMul) returns 0
   * Test multiply(fixed1()/mulPrecision(),fixed1()*mulPrecision()) returns fixed1()
   * Test multiply(maxFixedMul,maxFixedMul) is around maxUint256()
   * Test multiply(maxFixedMul+1,maxFixedMul+1) fails
   */
  // solhint-disable-next-line code-complexity
  function multiply(Fraction memory x, Fraction memory y) internal pure returns (Fraction memory) {
    if (x.value == 0 || y.value == 0) return Fraction(0);
    if (y.value == FIXED1_UINT) return x;
    if (x.value == FIXED1_UINT) return y;

    // Separate into integer and fractional parts
    // x = x1 + x2, y = y1 + y2
    uint256 x1 = integer(x).value / FIXED1_UINT;
    uint256 x2 = fractional(x).value;
    uint256 y1 = integer(y).value / FIXED1_UINT;
    uint256 y2 = fractional(y).value;

    // (x1 + x2) * (y1 + y2) = (x1 * y1) + (x1 * y2) + (x2 * y1) + (x2 * y2)
    uint256 x1y1 = x1 * y1;
    if (x1 != 0) require(x1y1 / x1 == y1, "overflow x1y1 detected");

    // x1y1 needs to be multiplied back by fixed1
    // solhint-disable-next-line var-name-mixedcase
    uint256 fixed_x1y1 = x1y1 * FIXED1_UINT;
    if (x1y1 != 0) require(fixed_x1y1 / x1y1 == FIXED1_UINT, "overflow x1y1 * fixed1 detected");
    x1y1 = fixed_x1y1;

    uint256 x2y1 = x2 * y1;
    if (x2 != 0) require(x2y1 / x2 == y1, "overflow x2y1 detected");

    uint256 x1y2 = x1 * y2;
    if (x1 != 0) require(x1y2 / x1 == y2, "overflow x1y2 detected");

    x2 = x2 / mulPrecision();
    y2 = y2 / mulPrecision();
    uint256 x2y2 = x2 * y2;
    if (x2 != 0) require(x2y2 / x2 == y2, "overflow x2y2 detected");

    // result = fixed1() * x1 * y1 + x1 * y2 + x2 * y1 + x2 * y2 / fixed1();
    Fraction memory result = Fraction(x1y1);
    result = add(result, Fraction(x2y1)); // Add checks for overflow
    result = add(result, Fraction(x1y2)); // Add checks for overflow
    result = add(result, Fraction(x2y2)); // Add checks for overflow
    return result;
  }

  /**
   * @notice 1/x
   * @dev
   * Test reciprocal(0) fails
   * Test reciprocal(fixed1()) returns fixed1()
   * Test reciprocal(fixed1()*fixed1()) returns 1 // Testing how the fractional is truncated
   * Test reciprocal(1+fixed1()*fixed1()) returns 0 // Testing how the fractional is truncated
   * Test reciprocal(newFixedFraction(1, 1e24)) returns newFixed(1e24)
   */
  function reciprocal(Fraction memory x) internal pure returns (Fraction memory) {
    require(x.value != 0, "can't call reciprocal(0)");
    return Fraction((FIXED1_UINT * FIXED1_UINT) / x.value); // Can't overflow
  }

  /**
   * @notice x/y. If the dividend is higher than the max dividend value, it
   * might overflow. You can use multiply(x,reciprocal(y)) instead.
   * @dev The maximum value that can be safely used as a dividend (maxNewFixed) is defined as
   * divide(maxNewFixed,newFixedFraction(1,fixed1())) is around maxUint256().
   * This yields the value 115792089237316195423570985008687907853269984665640564.
   * Test maxNewFixed equals maxUint256()/fixed1()
   * Test divide(maxNewFixed,1) equals maxNewFixed*(fixed1)
   * Test divide(maxNewFixed+1,multiply(mulPrecision(),mulPrecision())) throws
   * Test divide(fixed1(),0) fails
   * Test divide(maxNewFixed,1) = maxNewFixed*(10^digits())
   * Test divide(maxNewFixed+1,1) throws
   */
  function divide(Fraction memory x, Fraction memory y) internal pure returns (Fraction memory) {
    require(y.value != 0, "can't divide by 0");
    // solhint-disable-next-line var-name-mixedcase
    uint256 X = x.value * FIXED1_UINT;
    require(X / FIXED1_UINT == x.value, "overflow at divide");
    return Fraction(X / y.value);
  }

  /**
   * @notice x > y
   */
  function gt(Fraction memory x, Fraction memory y) internal pure returns (bool) {
    return x.value > y.value;
  }

  /**
   * @notice x >= y
   */
  function gte(Fraction memory x, Fraction memory y) internal pure returns (bool) {
    return x.value >= y.value;
  }

  /**
   * @notice x < y
   */
  function lt(Fraction memory x, Fraction memory y) internal pure returns (bool) {
    return x.value < y.value;
  }

  /**
   * @notice x <= y
   */
  function lte(Fraction memory x, Fraction memory y) internal pure returns (bool) {
    return x.value <= y.value;
  }

  /**
   * @notice x == y
   */
  function equals(Fraction memory x, Fraction memory y) internal pure returns (bool) {
    return x.value == y.value;
  }

  /**
   * @notice x <= 1
   */
  function isProperFraction(Fraction memory x) internal pure returns (bool) {
    return lte(x, fixed1());
  }
}
          

pragma solidity ^0.5.13;

contract CalledByVm {
  modifier onlyVm() {
    require(msg.sender == address(0), "Only VM can call");
    _;
  }
}
          

pragma solidity ^0.5.13;

import "openzeppelin-solidity/contracts/math/SafeMath.sol";
import "openzeppelin-solidity/contracts/ownership/Ownable.sol";
import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";

import "./interfaces/IStableToken.sol";
import "./interfaces/ICeloToken.sol";
import "./common/interfaces/ICeloVersionedContract.sol";
import "./common/CalledByVm.sol";
import "./common/Initializable.sol";
import "./common/FixidityLib.sol";
import "./common/Freezable.sol";
import "./common/UsingRegistry.sol";
import "./common/UsingPrecompiles.sol";

/**
 * @title An ERC20 compliant token with adjustable supply.
 */
// solhint-disable-next-line max-line-length
contract StableToken is
  ICeloVersionedContract,
  Ownable,
  Initializable,
  UsingRegistry,
  UsingPrecompiles,
  Freezable,
  CalledByVm,
  IStableToken,
  IERC20,
  ICeloToken
{
  using FixidityLib for FixidityLib.Fraction;
  using SafeMath for uint256;

  event InflationFactorUpdated(uint256 factor, uint256 lastUpdated);

  event InflationParametersUpdated(uint256 rate, uint256 updatePeriod, uint256 lastUpdated);

  event Transfer(address indexed from, address indexed to, uint256 value);

  event TransferComment(string comment);

  bytes32 private constant GRANDA_MENTO_REGISTRY_ID = keccak256(abi.encodePacked("GrandaMento"));
  bytes32 private constant BROKER_REGISTRY_ID = keccak256(abi.encodePacked("Broker"));

  string internal name_;
  string internal symbol_;
  uint8 internal decimals_;

  // Stored as units. Value can be found using unitsToValue().
  mapping(address => uint256) internal balances;
  uint256 internal totalSupply_;

  // Stored as values. Units can be found using valueToUnits().
  mapping(address => mapping(address => uint256)) internal allowed;

  // STABILITY FEE PARAMETERS

  // The `rate` is how much the `factor` is adjusted by per `updatePeriod`.
  // The `factor` describes units/value of StableToken, and is greater than or equal to 1.
  // The `updatePeriod` governs how often the `factor` is updated.
  // `factorLastUpdated` indicates when the inflation factor was last updated.
  struct InflationState {
    FixidityLib.Fraction rate;
    FixidityLib.Fraction factor;
    uint256 updatePeriod;
    uint256 factorLastUpdated;
  }

  // solhint-disable-next-line state-visibility
  InflationState inflationState;

  // The registry ID of the exchange contract with permission to mint and burn this token.
  // Unique per StableToken instance.
  // solhint-disable-next-line state-visibility
  bytes32 exchangeRegistryId;

  /**
   * @notice Recomputes and updates inflation factor if more than `updatePeriod`
   * has passed since last update.
   */
  modifier updateInflationFactor() {
    FixidityLib.Fraction memory updatedInflationFactor;
    uint256 lastUpdated;

    (updatedInflationFactor, lastUpdated) = getUpdatedInflationFactor();

    if (lastUpdated != inflationState.factorLastUpdated) {
      inflationState.factor = updatedInflationFactor;
      inflationState.factorLastUpdated = lastUpdated;
      emit InflationFactorUpdated(inflationState.factor.unwrap(), inflationState.factorLastUpdated);
    }
    _;
  }

  /**
   * @notice Returns the storage, major, minor, and patch version of the contract.
   * @return Storage version of the contract.
   * @return Major version of the contract.
   * @return Minor version of the contract.
   * @return Patch version of the contract.
   */
  function getVersionNumber()
    external
    pure
    returns (
      uint256,
      uint256,
      uint256,
      uint256
    )
  {
    return (1, 2, 0, 1);
  }

  /**
   * @notice Sets initialized == true on implementation contracts
   * @param test Set to true to skip implementation initialization
   */
  constructor(bool test) public Initializable(test) {}

  /**
   * @param _name The name of the stable token (English)
   * @param _symbol A short symbol identifying the token (e.g. "cUSD")
   * @param _decimals Tokens are divisible to this many decimal places.
   * @param registryAddress Address of the Registry contract.
   * @param inflationRate Weekly inflation rate.
   * @param inflationFactorUpdatePeriod How often the inflation factor is updated, in seconds.
   * @param initialBalanceAddresses Array of addresses with an initial balance.
   * @param initialBalanceValues Array of balance values corresponding to initialBalanceAddresses.
   * @param exchangeIdentifier String identifier of exchange in registry (for specific fiat pairs)
   */
  function initialize(
    string calldata _name,
    string calldata _symbol,
    uint8 _decimals,
    address registryAddress,
    uint256 inflationRate,
    uint256 inflationFactorUpdatePeriod,
    address[] calldata initialBalanceAddresses,
    uint256[] calldata initialBalanceValues,
    string calldata exchangeIdentifier
  ) external initializer {
    require(inflationRate != 0, "Must provide a non-zero inflation rate");
    require(inflationFactorUpdatePeriod > 0, "inflationFactorUpdatePeriod must be > 0");

    _transferOwnership(msg.sender);

    totalSupply_ = 0;
    name_ = _name;
    symbol_ = _symbol;
    decimals_ = _decimals;

    inflationState.rate = FixidityLib.wrap(inflationRate);
    inflationState.factor = FixidityLib.fixed1();
    inflationState.updatePeriod = inflationFactorUpdatePeriod;
    // solhint-disable-next-line not-rely-on-time
    inflationState.factorLastUpdated = now;

    require(initialBalanceAddresses.length == initialBalanceValues.length, "Array length mismatch");
    for (uint256 i = 0; i < initialBalanceAddresses.length; i = i.add(1)) {
      _mint(initialBalanceAddresses[i], initialBalanceValues[i]);
    }
    setRegistry(registryAddress);
    exchangeRegistryId = keccak256(abi.encodePacked(exchangeIdentifier));
  }

  /**
   * @notice Updates Inflation Parameters.
   * @param rate New rate.
   * @param updatePeriod How often inflationFactor is updated.
   */
  function setInflationParameters(uint256 rate, uint256 updatePeriod) external onlyOwner updateInflationFactor {
    require(rate != 0, "Must provide a non-zero inflation rate.");
    require(updatePeriod > 0, "updatePeriod must be > 0");
    inflationState.rate = FixidityLib.wrap(rate);
    inflationState.updatePeriod = updatePeriod;

    emit InflationParametersUpdated(
      rate,
      updatePeriod,
      // solhint-disable-next-line not-rely-on-time
      now
    );
  }

  /**
   * @notice Increase the allowance of another user.
   * @param spender The address which is being approved to spend StableToken.
   * @param value The increment of the amount of StableToken approved to the spender.
   * @return True if the transaction succeeds.
   */
  function increaseAllowance(address spender, uint256 value) external updateInflationFactor returns (bool) {
    require(spender != address(0), "reserved address 0x0 cannot have allowance");
    uint256 oldValue = allowed[msg.sender][spender];
    uint256 newValue = oldValue.add(value);
    allowed[msg.sender][spender] = newValue;
    emit Approval(msg.sender, spender, newValue);
    return true;
  }

  /**
   * @notice Decrease the allowance of another user.
   * @param spender The address which is being approved to spend StableToken.
   * @param value The decrement of the amount of StableToken approved to the spender.
   * @return True if the transaction succeeds.
   */
  function decreaseAllowance(address spender, uint256 value) external updateInflationFactor returns (bool) {
    uint256 oldValue = allowed[msg.sender][spender];
    uint256 newValue = oldValue.sub(value);
    allowed[msg.sender][spender] = newValue;
    emit Approval(msg.sender, spender, newValue);
    return true;
  }

  /**
   * @notice Approve a user to transfer StableToken on behalf of another user.
   * @param spender The address which is being approved to spend StableToken.
   * @param value The amount of StableToken approved to the spender.
   * @return True if the transaction succeeds.
   */
  function approve(address spender, uint256 value) external updateInflationFactor returns (bool) {
    require(spender != address(0), "reserved address 0x0 cannot have allowance");
    allowed[msg.sender][spender] = value;
    emit Approval(msg.sender, spender, value);
    return true;
  }

  /**
   * @notice Mints new StableToken and gives it to 'to'.
   * @param to The account for which to mint tokens.
   * @param value The amount of StableToken to mint.
   */
  function mint(address to, uint256 value) external updateInflationFactor returns (bool) {
    require(
      msg.sender == registry.getAddressForOrDie(getExchangeRegistryId()) ||
        msg.sender == registry.getAddressFor(VALIDATORS_REGISTRY_ID) ||
        msg.sender == registry.getAddressFor(GRANDA_MENTO_REGISTRY_ID) ||
        msg.sender == registry.getAddressFor(BROKER_REGISTRY_ID),
      "Sender not authorized to mint"
    );
    return _mint(to, value);
  }

  /**
   * @notice Mints new StableToken and gives it to 'to'.
   * @param to The account for which to mint tokens.
   * @param value The amount of StableToken to mint.
   */
  function _mint(address to, uint256 value) private returns (bool) {
    require(to != address(0), "0 is a reserved address");
    if (value == 0) {
      return true;
    }

    uint256 units = _valueToUnits(inflationState.factor, value);
    totalSupply_ = totalSupply_.add(units);
    balances[to] = balances[to].add(units);
    emit Transfer(address(0), to, value);
    return true;
  }

  /**
   * @notice Transfer token for a specified address
   * @param to The address to transfer to.
   * @param value The amount to be transferred.
   * @param comment The transfer comment.
   * @return True if the transaction succeeds.
   */
  function transferWithComment(
    address to,
    uint256 value,
    string calldata comment
  ) external updateInflationFactor onlyWhenNotFrozen returns (bool) {
    bool succeeded = transfer(to, value);
    emit TransferComment(comment);
    return succeeded;
  }

  /**
   * @notice Burns StableToken from the balance of msg.sender.
   * @param value The amount of StableToken to burn.
   */
  function burn(uint256 value) external updateInflationFactor returns (bool) {
    require(
      msg.sender == registry.getAddressForOrDie(getExchangeRegistryId()) ||
        msg.sender == registry.getAddressFor(GRANDA_MENTO_REGISTRY_ID) ||
        msg.sender == registry.getAddressFor(BROKER_REGISTRY_ID),
      "Sender not authorized to burn"
    );
    uint256 units = _valueToUnits(inflationState.factor, value);
    require(units <= balances[msg.sender], "value exceeded balance of sender");
    totalSupply_ = totalSupply_.sub(units);
    balances[msg.sender] = balances[msg.sender].sub(units);
    emit Transfer(msg.sender, address(0), units);
    return true;
  }

  /**
   * @notice Transfers StableToken from one address to another on behalf of a user.
   * @param from The address to transfer StableToken from.
   * @param to The address to transfer StableToken to.
   * @param value The amount of StableToken to transfer.
   * @return True if the transaction succeeds.
   */
  function transferFrom(
    address from,
    address to,
    uint256 value
  ) external updateInflationFactor onlyWhenNotFrozen returns (bool) {
    uint256 units = _valueToUnits(inflationState.factor, value);
    require(to != address(0), "transfer attempted to reserved address 0x0");
    require(units <= balances[from], "transfer value exceeded balance of sender");
    require(value <= allowed[from][msg.sender], "transfer value exceeded sender's allowance for recipient");

    balances[to] = balances[to].add(units);
    balances[from] = balances[from].sub(units);
    allowed[from][msg.sender] = allowed[from][msg.sender].sub(value);
    emit Transfer(from, to, value);
    return true;
  }

  /**
   * @return The name of the stable token.
   */
  function name() external view returns (string memory) {
    return name_;
  }

  /**
   * @return The symbol of the stable token.
   */
  function symbol() external view returns (string memory) {
    return symbol_;
  }

  /**
   * @return The number of decimal places to which StableToken is divisible.
   */
  function decimals() external view returns (uint8) {
    return decimals_;
  }

  /**
   * @notice Gets the amount of owner's StableToken allowed to be spent by spender.
   * @param accountOwner The owner of the StableToken.
   * @param spender The spender of the StableToken.
   * @return The amount of StableToken owner is allowing spender to spend.
   */
  function allowance(address accountOwner, address spender) external view returns (uint256) {
    return allowed[accountOwner][spender];
  }

  /**
   * @notice Gets the balance of the specified address using the presently stored inflation factor.
   * @param accountOwner The address to query the balance of.
   * @return The balance of the specified address.
   */
  function balanceOf(address accountOwner) external view returns (uint256) {
    return unitsToValue(balances[accountOwner]);
  }

  /**
   * @return The total value of StableToken in existence
   * @dev Though totalSupply_ is stored in units, this returns value.
   */
  function totalSupply() external view returns (uint256) {
    return unitsToValue(totalSupply_);
  }

  /**
   * @notice gets inflation parameters.
   * @return rate
   * @return factor
   * @return updatePeriod
   * @return factorLastUpdated
   */
  function getInflationParameters()
    external
    view
    returns (
      uint256,
      uint256,
      uint256,
      uint256
    )
  {
    return (
      inflationState.rate.unwrap(),
      inflationState.factor.unwrap(),
      inflationState.updatePeriod,
      inflationState.factorLastUpdated
    );
  }

  /**
   * @notice Returns the units for a given value given the current inflation factor.
   * @param value The value to convert to units.
   * @return The units corresponding to `value` given the current inflation factor.
   * @dev We don't compute the updated inflationFactor here because
   * we assume any function calling this will have updated the inflation factor.
   */
  function valueToUnits(uint256 value) external view returns (uint256) {
    FixidityLib.Fraction memory updatedInflationFactor;

    (updatedInflationFactor, ) = getUpdatedInflationFactor();
    return _valueToUnits(updatedInflationFactor, value);
  }

  /**
   * @notice Returns the exchange id in the registry of the corresponding fiat pair exchange.
   * @dev When this storage is uninitialized, it falls back to the default EXCHANGE_REGISTRY_ID.
   * exchangeRegistryId was introduced after the initial release of cUSD's StableToken,
   * so exchangeRegistryId will be uninitialized for that contract. If cUSD's StableToken
   * exchangeRegistryId were to be correctly initialized, this function could be deprecated
   * in favor of using exchangeRegistryId directly.
   * @return Registry id for the corresponding exchange.
   */
  function getExchangeRegistryId() public view returns (bytes32) {
    if (exchangeRegistryId == bytes32(0)) {
      return EXCHANGE_REGISTRY_ID;
    } else {
      return exchangeRegistryId;
    }
  }

  /**
   * @notice Returns the value of a given number of units given the current inflation factor.
   * @param units The units to convert to value.
   * @return The value corresponding to `units` given the current inflation factor.
   */
  function unitsToValue(uint256 units) public view returns (uint256) {
    FixidityLib.Fraction memory updatedInflationFactor;

    (updatedInflationFactor, ) = getUpdatedInflationFactor();

    // We're ok using FixidityLib.divide here because updatedInflationFactor is
    // not going to surpass maxFixedDivisor any time soon.
    // Quick upper-bound estimation: if annual inflation were 5% (an order of
    // magnitude more than the initial proposal of 0.5%), in 500 years, the
    // inflation factor would be on the order of 10**10, which is still a safe
    // divisor.
    return FixidityLib.newFixed(units).divide(updatedInflationFactor).fromFixed();
  }

  /**
   * @notice Returns the units for a given value given the current inflation factor.
   * @param inflationFactor The current inflation factor.
   * @param value The value to convert to units.
   * @return The units corresponding to `value` given the current inflation factor.
   * @dev We assume any function calling this will have updated the inflation factor.
   */
  function _valueToUnits(FixidityLib.Fraction memory inflationFactor, uint256 value) private pure returns (uint256) {
    return inflationFactor.multiply(FixidityLib.newFixed(value)).fromFixed();
  }

  /**
   * @notice Computes the up-to-date inflation factor.
   * @return Current inflation factor.
   * @return Last time when the returned inflation factor was updated.
   */
  function getUpdatedInflationFactor() private view returns (FixidityLib.Fraction memory, uint256) {
    /* solhint-disable not-rely-on-time */
    if (now < inflationState.factorLastUpdated.add(inflationState.updatePeriod)) {
      return (inflationState.factor, inflationState.factorLastUpdated);
    }

    uint256 numerator;
    uint256 denominator;

    // TODO: handle retroactive updates given decreases to updatePeriod
    uint256 timesToApplyInflation = now.sub(inflationState.factorLastUpdated).div(inflationState.updatePeriod);

    (numerator, denominator) = fractionMulExp(
      inflationState.factor.unwrap(),
      FixidityLib.fixed1().unwrap(),
      inflationState.rate.unwrap(),
      FixidityLib.fixed1().unwrap(),
      timesToApplyInflation,
      decimals_
    );

    // This should never happen. If something went wrong updating the
    // inflation factor, keep the previous factor
    if (numerator == 0 || denominator == 0) {
      return (inflationState.factor, inflationState.factorLastUpdated);
    }

    FixidityLib.Fraction memory currentInflationFactor = FixidityLib.wrap(numerator).divide(
      FixidityLib.wrap(denominator)
    );
    uint256 lastUpdated = inflationState.factorLastUpdated.add(inflationState.updatePeriod.mul(timesToApplyInflation));

    return (currentInflationFactor, lastUpdated);
    /* solhint-enable not-rely-on-time */
  }

  /**
   * @notice Transfers `value` from `msg.sender` to `to`
   * @param to The address to transfer to.
   * @param value The amount to be transferred.
   */
  // solhint-disable-next-line no-simple-event-func-name
  function transfer(address to, uint256 value) public updateInflationFactor onlyWhenNotFrozen returns (bool) {
    return _transfer(to, value);
  }

  /**
   * @notice Transfers StableToken from one address to another
   * @param to The address to transfer StableToken to.
   * @param value The amount of StableToken to be transferred.
   */
  function _transfer(address to, uint256 value) internal returns (bool) {
    require(to != address(0), "transfer attempted to reserved address 0x0");
    uint256 units = _valueToUnits(inflationState.factor, value);
    require(balances[msg.sender] >= units, "transfer value exceeded balance of sender");
    balances[msg.sender] = balances[msg.sender].sub(units);
    balances[to] = balances[to].add(units);
    emit Transfer(msg.sender, to, value);
    return true;
  }

  /**
   * @notice Reserve balance for making payments for gas in this StableToken currency.
   * @param from The account to reserve balance from
   * @param value The amount of balance to reserve
   * @dev Note that this function is called by the protocol when paying for tx fees in this
   * currency. After the tx is executed, gas is refunded to the sender and credited to the
   * various tx fee recipients via a call to `creditGasFees`. Note too that the events emitted
   * by `creditGasFees` reflect the *net* gas fee payments for the transaction.
   */
  function debitGasFees(address from, uint256 value) external onlyVm onlyWhenNotFrozen updateInflationFactor {
    uint256 units = _valueToUnits(inflationState.factor, value);
    balances[from] = balances[from].sub(units);
    totalSupply_ = totalSupply_.sub(units);
  }

  /**
   * @notice Alternative function to credit balance after making payments
   * for gas in this StableToken currency.
   * @param from The account to debit balance from
   * @param feeRecipient Coinbase address
   * @param gatewayFeeRecipient Gateway address
   * @param communityFund Community fund address
   * @param tipTxFee Coinbase fee
   * @param baseTxFee Community fund fee
   * @param gatewayFee Gateway fee
   * @dev Note that this function is called by the protocol when paying for tx fees in this
   * currency. Before the tx is executed, gas is debited from the sender via a call to
   * `debitGasFees`. Note too that the events emitted by `creditGasFees` reflect the *net* gas fee
   * payments for the transaction.
   */
  function creditGasFees(
    address from,
    address feeRecipient,
    address gatewayFeeRecipient,
    address communityFund,
    uint256 refund,
    uint256 tipTxFee,
    uint256 gatewayFee,
    uint256 baseTxFee
  ) external onlyVm onlyWhenNotFrozen {
    uint256 units = _valueToUnits(inflationState.factor, refund);
    balances[from] = balances[from].add(units);

    units = units.add(_creditGas(from, communityFund, baseTxFee));
    units = units.add(_creditGas(from, feeRecipient, tipTxFee));
    units = units.add(_creditGas(from, gatewayFeeRecipient, gatewayFee));
    totalSupply_ = totalSupply_.add(units);
  }

  function _creditGas(
    address from,
    address to,
    uint256 value
  ) internal returns (uint256) {
    if (to == address(0)) {
      return 0;
    }
    uint256 units = _valueToUnits(inflationState.factor, value);
    balances[to] = balances[to].add(units);
    emit Transfer(from, to, value);
    return units;
  }
}