// File: @openzeppelin/contracts/math/SafeMath.sol

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
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);
}

// File: @openzeppelin/contracts/utils/Address.sol



pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/SafeERC20.sol



pragma solidity >=0.6.0 <0.8.0;




/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: solidity/contracts/converter/ConverterVersion.sol


pragma solidity 0.6.12;

contract ConverterVersion {
    uint16 public constant version = 46;
}

// File: solidity/contracts/utility/interfaces/IOwned.sol


pragma solidity 0.6.12;

/*
    Owned contract interface
*/
interface IOwned {
    // this function isn't since the compiler emits automatically generated getter functions as external
    function owner() external view returns (address);

    function transferOwnership(address _newOwner) external;

    function acceptOwnership() external;
}

// File: solidity/contracts/converter/interfaces/IConverterAnchor.sol


pragma solidity 0.6.12;


/*
    Converter Anchor interface
*/
interface IConverterAnchor is IOwned {

}

// File: solidity/contracts/converter/interfaces/IConverter.sol


pragma solidity 0.6.12;




/*
    Converter interface
*/
interface IConverter is IOwned {
    function converterType() external pure returns (uint16);

    function anchor() external view returns (IConverterAnchor);

    function isActive() external view returns (bool);

    function targetAmountAndFee(
        IERC20 _sourceToken,
        IERC20 _targetToken,
        uint256 _amount
    ) external view returns (uint256, uint256);

    function convert(
        IERC20 _sourceToken,
        IERC20 _targetToken,
        uint256 _amount,
        address _trader,
        address payable _beneficiary
    ) external payable returns (uint256);

    function conversionFee() external view returns (uint32);

    function maxConversionFee() external view returns (uint32);

    function reserveBalance(IERC20 _reserveToken) external view returns (uint256);

    receive() external payable;

    function transferAnchorOwnership(address _newOwner) external;

    function acceptAnchorOwnership() external;

    function setConversionFee(uint32 _conversionFee) external;

    function addReserve(IERC20 _token, uint32 _weight) external;

    function transferReservesOnUpgrade(address _newConverter) external;

    function onUpgradeComplete() external;

    // deprecated, backward compatibility
    function token() external view returns (IConverterAnchor);

    function transferTokenOwnership(address _newOwner) external;

    function acceptTokenOwnership() external;

    function connectors(IERC20 _address)
        external
        view
        returns (
            uint256,
            uint32,
            bool,
            bool,
            bool
        );

    function getConnectorBalance(IERC20 _connectorToken) external view returns (uint256);

    function connectorTokens(uint256 _index) external view returns (IERC20);

    function connectorTokenCount() external view returns (uint16);

    /**
     * @dev triggered when the converter is activated
     *
     * @param _type        converter type
     * @param _anchor      converter anchor
     * @param _activated   true if the converter was activated, false if it was deactivated
     */
    event Activation(uint16 indexed _type, IConverterAnchor indexed _anchor, bool indexed _activated);

    /**
     * @dev triggered when a conversion between two tokens occurs
     *
     * @param _fromToken       source ERC20 token
     * @param _toToken         target ERC20 token
     * @param _trader          wallet that initiated the trade
     * @param _amount          input amount in units of the source token
     * @param _return          output amount minus conversion fee in units of the target token
     * @param _conversionFee   conversion fee in units of the target token
     */
    event Conversion(
        IERC20 indexed _fromToken,
        IERC20 indexed _toToken,
        address indexed _trader,
        uint256 _amount,
        uint256 _return,
        int256 _conversionFee
    );

    /**
     * @dev triggered when the rate between two tokens in the converter changes
     * note that the event might be dispatched for rate updates between any two tokens in the converter
     *
     * @param  _token1 address of the first token
     * @param  _token2 address of the second token
     * @param  _rateN  rate of 1 unit of `_token1` in `_token2` (numerator)
     * @param  _rateD  rate of 1 unit of `_token1` in `_token2` (denominator)
     */
    event TokenRateUpdate(IERC20 indexed _token1, IERC20 indexed _token2, uint256 _rateN, uint256 _rateD);

    /**
     * @dev triggered when the conversion fee is updated
     *
     * @param  _prevFee    previous fee percentage, represented in ppm
     * @param  _newFee     new fee percentage, represented in ppm
     */
    event ConversionFeeUpdate(uint32 _prevFee, uint32 _newFee);
}

// File: solidity/contracts/converter/interfaces/IConverterUpgrader.sol


pragma solidity 0.6.12;

/*
    Converter Upgrader interface
*/
interface IConverterUpgrader {
    function upgrade(bytes32 _version) external;

    function upgrade(uint16 _version) external;
}

// File: solidity/contracts/utility/interfaces/ITokenHolder.sol


pragma solidity 0.6.12;



/*
    Token Holder interface
*/
interface ITokenHolder is IOwned {
    receive() external payable;

    function withdrawTokens(
        IERC20 token,
        address payable to,
        uint256 amount
    ) external;

    function withdrawTokensMultiple(
        IERC20[] calldata tokens,
        address payable to,
        uint256[] calldata amounts
    ) external;
}

// File: solidity/contracts/INetworkSettings.sol


pragma solidity 0.6.12;


interface INetworkSettings {
    function networkFeeParams() external view returns (ITokenHolder, uint32);

    function networkFeeWallet() external view returns (ITokenHolder);

    function networkFee() external view returns (uint32);
}

// File: solidity/contracts/token/interfaces/IDSToken.sol


pragma solidity 0.6.12;




/*
    DSToken interface
*/
interface IDSToken is IConverterAnchor, IERC20 {
    function issue(address _to, uint256 _amount) external;

    function destroy(address _from, uint256 _amount) external;
}

// File: solidity/contracts/utility/MathEx.sol


pragma solidity 0.6.12;

/**
 * @dev This library provides a set of complex math operations.
 */
library MathEx {
    uint256 private constant MAX_EXP_BIT_LEN = 4;
    uint256 private constant MAX_EXP = 2**MAX_EXP_BIT_LEN - 1;
    uint256 private constant MAX_UINT128 = 2**128 - 1;

    /**
     * @dev returns the largest integer smaller than or equal to the square root of a positive integer
     *
     * @param _num a positive integer
     *
     * @return the largest integer smaller than or equal to the square root of the positive integer
     */
    function floorSqrt(uint256 _num) internal pure returns (uint256) {
        uint256 x = _num / 2 + 1;
        uint256 y = (x + _num / x) / 2;
        while (x > y) {
            x = y;
            y = (x + _num / x) / 2;
        }
        return x;
    }

    /**
     * @dev returns the smallest integer larger than or equal to the square root of a positive integer
     *
     * @param _num a positive integer
     *
     * @return the smallest integer larger than or equal to the square root of the positive integer
     */
    function ceilSqrt(uint256 _num) internal pure returns (uint256) {
        uint256 x = floorSqrt(_num);
        return x * x == _num ? x : x + 1;
    }

    /**
     * @dev computes a powered ratio
     *
     * @param _n   ratio numerator
     * @param _d   ratio denominator
     * @param _exp ratio exponent
     *
     * @return powered ratio's numerator and denominator
     */
    function poweredRatio(
        uint256 _n,
        uint256 _d,
        uint256 _exp
    ) internal pure returns (uint256, uint256) {
        require(_exp <= MAX_EXP, "ERR_EXP_TOO_LARGE");

        uint256[MAX_EXP_BIT_LEN] memory ns;
        uint256[MAX_EXP_BIT_LEN] memory ds;

        (ns[0], ds[0]) = reducedRatio(_n, _d, MAX_UINT128);
        for (uint256 i = 0; (_exp >> i) > 1; i++) {
            (ns[i + 1], ds[i + 1]) = reducedRatio(ns[i] ** 2, ds[i] ** 2, MAX_UINT128);
        }

        uint256 n = 1;
        uint256 d = 1;

        for (uint256 i = 0; (_exp >> i) > 0; i++) {
            if (((_exp >> i) & 1) > 0) {
                (n, d) = reducedRatio(n * ns[i], d * ds[i], MAX_UINT128);
            }
        }

        return (n, d);
    }

    /**
     * @dev computes a reduced-scalar ratio
     *
     * @param _n   ratio numerator
     * @param _d   ratio denominator
     * @param _max maximum desired scalar
     *
     * @return ratio's numerator and denominator
     */
    function reducedRatio(
        uint256 _n,
        uint256 _d,
        uint256 _max
    ) internal pure returns (uint256, uint256) {
        (uint256 n, uint256 d) = (_n, _d);
        if (n > _max || d > _max) {
            (n, d) = normalizedRatio(n, d, _max);
        }
        if (n != d) {
            return (n, d);
        }
        return (1, 1);
    }

    /**
     * @dev computes "scale * a / (a + b)" and "scale * b / (a + b)".
     */
    function normalizedRatio(
        uint256 _a,
        uint256 _b,
        uint256 _scale
    ) internal pure returns (uint256, uint256) {
        if (_a <= _b) {
            return accurateRatio(_a, _b, _scale);
        }
        (uint256 y, uint256 x) = accurateRatio(_b, _a, _scale);
        return (x, y);
    }

    /**
     * @dev computes "scale * a / (a + b)" and "scale * b / (a + b)", assuming that "a <= b".
     */
    function accurateRatio(
        uint256 _a,
        uint256 _b,
        uint256 _scale
    ) internal pure returns (uint256, uint256) {
        uint256 maxVal = uint256(-1) / _scale;
        if (_a > maxVal) {
            uint256 c = _a / (maxVal + 1) + 1;
            _a /= c; // we can now safely compute `_a * _scale`
            _b /= c;
        }
        if (_a != _b) {
            uint256 n = _a * _scale;
            uint256 d = _a + _b; // can overflow
            if (d >= _a) {
                // no overflow in `_a + _b`
                uint256 x = roundDiv(n, d); // we can now safely compute `_scale - x`
                uint256 y = _scale - x;
                return (x, y);
            }
            if (n < _b - (_b - _a) / 2) {
                return (0, _scale); // `_a * _scale < (_a + _b) / 2 < MAX_UINT256 < _a + _b`
            }
            return (1, _scale - 1); // `(_a + _b) / 2 < _a * _scale < MAX_UINT256 < _a + _b`
        }
        return (_scale / 2, _scale / 2); // allow reduction to `(1, 1)` in the calling function
    }

    /**
     * @dev computes the nearest integer to a given quotient without overflowing or underflowing.
     */
    function roundDiv(uint256 _n, uint256 _d) internal pure returns (uint256) {
        return _n / _d + (_n % _d) / (_d - _d / 2);
    }

    /**
     * @dev returns the average number of decimal digits in a given list of positive integers
     *
     * @param _values  list of positive integers
     *
     * @return the average number of decimal digits in the given list of positive integers
     */
    function geometricMean(uint256[] memory _values) internal pure returns (uint256) {
        uint256 numOfDigits = 0;
        uint256 length = _values.length;
        for (uint256 i = 0; i < length; i++) {
            numOfDigits += decimalLength(_values[i]);
        }
        return uint256(10)**(roundDivUnsafe(numOfDigits, length) - 1);
    }

    /**
     * @dev returns the number of decimal digits in a given positive integer
     *
     * @param _x   positive integer
     *
     * @return the number of decimal digits in the given positive integer
     */
    function decimalLength(uint256 _x) internal pure returns (uint256) {
        uint256 y = 0;
        for (uint256 x = _x; x > 0; x /= 10) {
            y++;
        }
        return y;
    }

    /**
     * @dev returns the nearest integer to a given quotient
     * the computation is overflow-safe assuming that the input is sufficiently small
     *
     * @param _n   quotient numerator
     * @param _d   quotient denominator
     *
     * @return the nearest integer to the given quotient
     */
    function roundDivUnsafe(uint256 _n, uint256 _d) internal pure returns (uint256) {
        return (_n + _d / 2) / _d;
    }

    /**
     * @dev returns the larger of two values
     *
     * @param _val1 the first value
     * @param _val2 the second value
     */
    function max(uint256 _val1, uint256 _val2) internal pure returns (uint256) {
        return _val1 > _val2 ? _val1 : _val2;
    }
}

// File: solidity/contracts/utility/Owned.sol


pragma solidity 0.6.12;


/**
 * @dev This contract provides support and utilities for contract ownership.
 */
contract Owned is IOwned {
    address public override owner;
    address public newOwner;

    /**
     * @dev triggered when the owner is updated
     *
     * @param _prevOwner previous owner
     * @param _newOwner  new owner
     */
    event OwnerUpdate(address indexed _prevOwner, address indexed _newOwner);

    /**
     * @dev initializes a new Owned instance
     */
    constructor() public {
        owner = msg.sender;
    }

    // allows execution by the owner only
    modifier ownerOnly {
        _ownerOnly();
        _;
    }

    // error message binary size optimization
    function _ownerOnly() internal view {
        require(msg.sender == owner, "ERR_ACCESS_DENIED");
    }

    /**
     * @dev allows transferring the contract ownership
     * the new owner still needs to accept the transfer
     * can only be called by the contract owner
     *
     * @param _newOwner    new contract owner
     */
    function transferOwnership(address _newOwner) public override ownerOnly {
        require(_newOwner != owner, "ERR_SAME_OWNER");
        newOwner = _newOwner;
    }

    /**
     * @dev used by a new owner to accept an ownership transfer
     */
    function acceptOwnership() public override {
        require(msg.sender == newOwner, "ERR_ACCESS_DENIED");
        emit OwnerUpdate(owner, newOwner);
        owner = newOwner;
        newOwner = address(0);
    }
}

// File: solidity/contracts/utility/Utils.sol


pragma solidity 0.6.12;


/**
 * @dev Utilities & Common Modifiers
 */
contract Utils {
    uint32 internal constant PPM_RESOLUTION = 1000000;
    IERC20 internal constant NATIVE_TOKEN_ADDRESS = IERC20(0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE);

    // verifies that a value is greater than zero
    modifier greaterThanZero(uint256 _value) {
        _greaterThanZero(_value);
        _;
    }

    // error message binary size optimization
    function _greaterThanZero(uint256 _value) internal pure {
        require(_value > 0, "ERR_ZERO_VALUE");
    }

    // validates an address - currently only checks that it isn't null
    modifier validAddress(address _address) {
        _validAddress(_address);
        _;
    }

    // error message binary size optimization
    function _validAddress(address _address) internal pure {
        require(_address != address(0), "ERR_INVALID_ADDRESS");
    }

    // ensures that the portion is valid
    modifier validPortion(uint32 _portion) {
        _validPortion(_portion);
        _;
    }

    // error message binary size optimization
    function _validPortion(uint32 _portion) internal pure {
        require(_portion > 0 && _portion <= PPM_RESOLUTION, "ERR_INVALID_PORTION");
    }

    // validates an external address - currently only checks that it isn't null or this
    modifier validExternalAddress(address _address) {
        _validExternalAddress(_address);
        _;
    }

    // error message binary size optimization
    function _validExternalAddress(address _address) internal view {
        require(_address != address(0) && _address != address(this), "ERR_INVALID_EXTERNAL_ADDRESS");
    }

    // ensures that the fee is valid
    modifier validFee(uint32 fee) {
        _validFee(fee);
        _;
    }

    // error message binary size optimization
    function _validFee(uint32 fee) internal pure {
        require(fee <= PPM_RESOLUTION, "ERR_INVALID_FEE");
    }
}

// File: solidity/contracts/utility/interfaces/IContractRegistry.sol


pragma solidity 0.6.12;

/*
    Contract Registry interface
*/
interface IContractRegistry {
    function addressOf(bytes32 _contractName) external view returns (address);
}

// File: solidity/contracts/utility/ContractRegistryClient.sol


pragma solidity 0.6.12;




/**
 * @dev This is the base contract for ContractRegistry clients.
 */
contract ContractRegistryClient is Owned, Utils {
    bytes32 internal constant CONTRACT_REGISTRY = "ContractRegistry";
    bytes32 internal constant BANCOR_NETWORK = "BancorNetwork";
    bytes32 internal constant BANCOR_FORMULA = "BancorFormula";
    bytes32 internal constant CONVERTER_FACTORY = "ConverterFactory";
    bytes32 internal constant CONVERSION_PATH_FINDER = "ConversionPathFinder";
    bytes32 internal constant CONVERTER_UPGRADER = "BancorConverterUpgrader";
    bytes32 internal constant CONVERTER_REGISTRY = "BancorConverterRegistry";
    bytes32 internal constant CONVERTER_REGISTRY_DATA = "BancorConverterRegistryData";
    bytes32 internal constant BNT_TOKEN = "BNTToken";
    bytes32 internal constant BANCOR_X = "BancorX";
    bytes32 internal constant BANCOR_X_UPGRADER = "BancorXUpgrader";
    bytes32 internal constant LIQUIDITY_PROTECTION = "LiquidityProtection";
    bytes32 internal constant NETWORK_SETTINGS = "NetworkSettings";

    IContractRegistry public registry; // address of the current contract-registry
    IContractRegistry public prevRegistry; // address of the previous contract-registry
    bool public onlyOwnerCanUpdateRegistry; // only an owner can update the contract-registry

    /**
     * @dev verifies that the caller is mapped to the given contract name
     *
     * @param _contractName    contract name
     */
    modifier only(bytes32 _contractName) {
        _only(_contractName);
        _;
    }

    // error message binary size optimization
    function _only(bytes32 _contractName) internal view {
        require(msg.sender == addressOf(_contractName), "ERR_ACCESS_DENIED");
    }

    /**
     * @dev initializes a new ContractRegistryClient instance
     *
     * @param  _registry   address of a contract-registry contract
     */
    constructor(IContractRegistry _registry) internal validAddress(address(_registry)) {
        registry = IContractRegistry(_registry);
        prevRegistry = IContractRegistry(_registry);
    }

    /**
     * @dev updates to the new contract-registry
     */
    function updateRegistry() public {
        // verify that this function is permitted
        require(msg.sender == owner || !onlyOwnerCanUpdateRegistry, "ERR_ACCESS_DENIED");

        // get the new contract-registry
        IContractRegistry newRegistry = IContractRegistry(addressOf(CONTRACT_REGISTRY));

        // verify that the new contract-registry is different and not zero
        require(newRegistry != registry && address(newRegistry) != address(0), "ERR_INVALID_REGISTRY");

        // verify that the new contract-registry is pointing to a non-zero contract-registry
        require(newRegistry.addressOf(CONTRACT_REGISTRY) != address(0), "ERR_INVALID_REGISTRY");

        // save a backup of the current contract-registry before replacing it
        prevRegistry = registry;

        // replace the current contract-registry with the new contract-registry
        registry = newRegistry;
    }

    /**
     * @dev restores the previous contract-registry
     */
    function restoreRegistry() public ownerOnly {
        // restore the previous contract-registry
        registry = prevRegistry;
    }

    /**
     * @dev restricts the permission to update the contract-registry
     *
     * @param _onlyOwnerCanUpdateRegistry  indicates whether or not permission is restricted to owner only
     */
    function restrictRegistryUpdate(bool _onlyOwnerCanUpdateRegistry) public ownerOnly {
        // change the permission to update the contract-registry
        onlyOwnerCanUpdateRegistry = _onlyOwnerCanUpdateRegistry;
    }

    /**
     * @dev returns the address associated with the given contract name
     *
     * @param _contractName    contract name
     *
     * @return contract address
     */
    function addressOf(bytes32 _contractName) internal view returns (address) {
        return registry.addressOf(_contractName);
    }
}

// File: solidity/contracts/utility/ReentrancyGuard.sol


pragma solidity 0.6.12;

/**
 * @dev This contract provides protection against calling a function
 * (directly or indirectly) from within itself.
 */
contract ReentrancyGuard {
    uint256 private constant UNLOCKED = 1;
    uint256 private constant LOCKED = 2;

    // LOCKED while protected code is being executed, UNLOCKED otherwise
    uint256 private state = UNLOCKED;

    /**
     * @dev ensures instantiation only by sub-contracts
     */
    constructor() internal {}

    // protects a function against reentrancy attacks
    modifier protected() {
        _protected();
        state = LOCKED;
        _;
        state = UNLOCKED;
    }

    // error message binary size optimization
    function _protected() internal view {
        require(state == UNLOCKED, "ERR_REENTRANCY");
    }
}

// File: solidity/contracts/utility/Time.sol


pragma solidity 0.6.12;

/*
    Time implementing contract
*/
contract Time {
    /**
     * @dev returns the current time
     */
    function time() internal view virtual returns (uint256) {
        return block.timestamp;
    }
}

// File: solidity/contracts/converter/types/standard-pool/StandardPoolConverter.sol


pragma solidity 0.6.12;













/**
 * @dev This contract is a specialized version of the converter, which is
 * optimized for a liquidity pool that has 2 reserves with 50%/50% weights.
 */
contract StandardPoolConverter is ConverterVersion, IConverter, ContractRegistryClient, ReentrancyGuard, Time {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;
    using MathEx for *;

    uint256 private constant MAX_UINT128 = 2**128 - 1;
    uint256 private constant MAX_UINT112 = 2**112 - 1;
    uint256 private constant MAX_UINT32 = 2**32 - 1;
    uint256 private constant AVERAGE_RATE_PERIOD = 10 minutes;

    uint256 private __reserveBalances;
    uint256 private _reserveBalancesProduct;
    IERC20[] private __reserveTokens;
    mapping(IERC20 => uint256) private __reserveIds;

    IConverterAnchor public override anchor; // converter anchor contract
    uint32 public override maxConversionFee; // maximum conversion fee, represented in ppm, 0...1000000
    uint32 public override conversionFee; // current conversion fee, represented in ppm, 0...maxConversionFee

    // average rate details:
    // bits 0...111 represent the numerator of the rate between reserve token 0 and reserve token 1
    // bits 111...223 represent the denominator of the rate between reserve token 0 and reserve token 1
    // bits 224...255 represent the update-time of the rate between reserve token 0 and reserve token 1
    // where `numerator / denominator` gives the worth of one reserve token 0 in units of reserve token 1
    uint256 public averageRateInfo;

    /**
     * @dev triggered after liquidity is added
     *
     * @param  _provider       liquidity provider
     * @param  _reserveToken   reserve token address
     * @param  _amount         reserve token amount
     * @param  _newBalance     reserve token new balance
     * @param  _newSupply      pool token new supply
     */
    event LiquidityAdded(
        address indexed _provider,
        IERC20 indexed _reserveToken,
        uint256 _amount,
        uint256 _newBalance,
        uint256 _newSupply
    );

    /**
     * @dev triggered after liquidity is removed
     *
     * @param  _provider       liquidity provider
     * @param  _reserveToken   reserve token address
     * @param  _amount         reserve token amount
     * @param  _newBalance     reserve token new balance
     * @param  _newSupply      pool token new supply
     */
    event LiquidityRemoved(
        address indexed _provider,
        IERC20 indexed _reserveToken,
        uint256 _amount,
        uint256 _newBalance,
        uint256 _newSupply
    );

    /**
     * @dev initializes a new StandardPoolConverter instance
     *
     * @param  _anchor             anchor governed by the converter
     * @param  _registry           address of a contract registry contract
     * @param  _maxConversionFee   maximum conversion fee, represented in ppm
     */
    constructor(
        IConverterAnchor _anchor,
        IContractRegistry _registry,
        uint32 _maxConversionFee
    ) public ContractRegistryClient(_registry) validAddress(address(_anchor)) validConversionFee(_maxConversionFee) {
        anchor = _anchor;
        maxConversionFee = _maxConversionFee;
    }

    // ensures that the converter is active
    modifier active() {
        _active();
        _;
    }

    // error message binary size optimization
    function _active() internal view {
        require(isActive(), "ERR_INACTIVE");
    }

    // ensures that the converter is not active
    modifier inactive() {
        _inactive();
        _;
    }

    // error message binary size optimization
    function _inactive() internal view {
        require(!isActive(), "ERR_ACTIVE");
    }

    // validates a reserve token address - verifies that the address belongs to one of the reserve tokens
    modifier validReserve(IERC20 _address) {
        _validReserve(_address);
        _;
    }

    // error message binary size optimization
    function _validReserve(IERC20 _address) internal view {
        require(__reserveIds[_address] != 0, "ERR_INVALID_RESERVE");
    }

    // validates conversion fee
    modifier validConversionFee(uint32 _conversionFee) {
        _validConversionFee(_conversionFee);
        _;
    }

    // error message binary size optimization
    function _validConversionFee(uint32 _conversionFee) internal pure {
        require(_conversionFee <= PPM_RESOLUTION, "ERR_INVALID_CONVERSION_FEE");
    }

    // validates reserve weight
    modifier validReserveWeight(uint32 _weight) {
        _validReserveWeight(_weight);
        _;
    }

    // error message binary size optimization
    function _validReserveWeight(uint32 _weight) internal pure {
        require(_weight == PPM_RESOLUTION / 2, "ERR_INVALID_RESERVE_WEIGHT");
    }

    /**
     * @dev returns the converter type
     *
     * @return see the converter types in the the main contract doc
     */
    function converterType() public pure virtual override returns (uint16) {
        return 3;
    }

    /**
     * @dev deposits ether
     * can only be called if the converter has an ETH reserve
     */
    receive() external payable override(IConverter) validReserve(NATIVE_TOKEN_ADDRESS) {}

    /**
     * @dev checks whether or not the converter version is 28 or higher
     *
     * @return true, since the converter version is 28 or higher
     */
    function isV28OrHigher() public pure returns (bool) {
        return true;
    }

    /**
     * @dev returns true if the converter is active, false otherwise
     *
     * @return true if the converter is active, false otherwise
     */
    function isActive() public view virtual override returns (bool) {
        return anchor.owner() == address(this);
    }

    /**
     * @dev transfers the anchor ownership
     * the new owner needs to accept the transfer
     * can only be called by the converter upgrader while the upgrader is the owner
     * note that prior to version 28, you should use 'transferAnchorOwnership' instead
     *
     * @param _newOwner    new token owner
     */
    function transferAnchorOwnership(address _newOwner) public override ownerOnly only(CONVERTER_UPGRADER) {
        anchor.transferOwnership(_newOwner);
    }

    /**
     * @dev accepts ownership of the anchor after an ownership transfer
     * most converters are also activated as soon as they accept the anchor ownership
     * can only be called by the contract owner
     * note that prior to version 28, you should use 'acceptTokenOwnership' instead
     */
    function acceptAnchorOwnership() public virtual override ownerOnly {
        // verify the the converter has exactly two reserves
        require(reserveTokenCount() == 2, "ERR_INVALID_RESERVE_COUNT");
        anchor.acceptOwnership();
        syncReserveBalances(0);
        emit Activation(converterType(), anchor, true);
    }

    /**
     * @dev updates the current conversion fee
     * can only be called by the contract owner
     *
     * @param _conversionFee new conversion fee, represented in ppm
     */
    function setConversionFee(uint32 _conversionFee) public override ownerOnly {
        require(_conversionFee <= maxConversionFee, "ERR_INVALID_CONVERSION_FEE");
        emit ConversionFeeUpdate(conversionFee, _conversionFee);
        conversionFee = _conversionFee;
    }

    /**
     * @dev transfers reserve balances to a new converter during an upgrade
     * can only be called by the converter upgraded which should be set at its owner
     *
     * @param _newConverter address of the converter to receive the new amount
     */
    function transferReservesOnUpgrade(address _newConverter)
        external
        override
        protected
        ownerOnly
        only(CONVERTER_UPGRADER)
    {
        uint256 reserveCount = __reserveTokens.length;
        for (uint256 i = 0; i < reserveCount; ++i) {
            IERC20 reserveToken = __reserveTokens[i];

            uint256 amount;
            if (reserveToken == NATIVE_TOKEN_ADDRESS) {
                amount = address(this).balance;
            } else {
                amount = reserveToken.balanceOf(address(this));
            }

            safeTransfer(reserveToken, _newConverter, amount);

            syncReserveBalance(reserveToken);
        }
    }

    /**
     * @dev upgrades the converter to the latest version
     * can only be called by the owner
     * note that the owner needs to call acceptOwnership on the new converter after the upgrade
     */
    function upgrade() public ownerOnly {
        IConverterUpgrader converterUpgrader = IConverterUpgrader(addressOf(CONVERTER_UPGRADER));

        // trigger de-activation event
        emit Activation(converterType(), anchor, false);

        transferOwnership(address(converterUpgrader));
        converterUpgrader.upgrade(version);
        acceptOwnership();
    }

    /**
     * @dev executed by the upgrader at the end of the upgrade process to handle custom pool logic
     */
    function onUpgradeComplete()
        external
        override
        protected
        ownerOnly
        only(CONVERTER_UPGRADER)
    {
        (uint256 reserveBalance0, uint256 reserveBalance1) = reserveBalances(1, 2);
        _reserveBalancesProduct = reserveBalance0 * reserveBalance1;
    }

    /**
     * @dev returns the number of reserve tokens
     * note that prior to version 17, you should use 'connectorTokenCount' instead
     *
     * @return number of reserve tokens
     */
    function reserveTokenCount() public view returns (uint16) {
        return uint16(__reserveTokens.length);
    }

    /**
     * @dev returns the array of reserve tokens
     *
     * @return array of reserve tokens
     */
    function reserveTokens() public view returns (IERC20[] memory) {
        return __reserveTokens;
    }

    /**
     * @dev defines a new reserve token for the converter
     * can only be called by the owner while the converter is inactive
     *
     * @param _token   address of the reserve token
     * @param _weight  reserve weight, represented in ppm, 1-1000000
     */
    function addReserve(IERC20 _token, uint32 _weight)
        public
        virtual
        override
        ownerOnly
        inactive
        validExternalAddress(address(_token))
        validReserveWeight(_weight)
    {
        // validate input
        require(address(_token) != address(anchor) && __reserveIds[_token] == 0, "ERR_INVALID_RESERVE");
        require(reserveTokenCount() < 2, "ERR_INVALID_RESERVE_COUNT");

        __reserveTokens.push(_token);
        __reserveIds[_token] = __reserveTokens.length;
    }

    /**
     * @dev returns the reserve's weight
     * added in version 28
     *
     * @param _reserveToken    reserve token contract address
     *
     * @return reserve weight
     */
    function reserveWeight(IERC20 _reserveToken) public view validReserve(_reserveToken) returns (uint32) {
        return PPM_RESOLUTION / 2;
    }

    /**
     * @dev returns the balance of a given reserve token
     *
     * @param _reserveToken    reserve token contract address
     *
     * @return the balance of the given reserve token
     */
    function reserveBalance(IERC20 _reserveToken) public view override returns (uint256) {
        uint256 reserveId = __reserveIds[_reserveToken];
        require(reserveId != 0, "ERR_INVALID_RESERVE");
        return reserveBalance(reserveId);
    }

    /**
     * @dev returns the balances of both reserve tokens
     *
     * @return the balances of both reserve tokens
     */
    function reserveBalances() public view returns (uint256, uint256) {
        return reserveBalances(1, 2);
    }

    /**
     * @dev syncs all stored reserve balances
     */
    function syncReserveBalances() external {
        syncReserveBalances(0);
    }

    /**
     * @dev calculates the accumulated network fee and transfers it to the network fee wallet
     */
    function processNetworkFees() external protected {
        (uint256 reserveBalance0, uint256 reserveBalance1) = processNetworkFees(0);
        _reserveBalancesProduct = reserveBalance0 * reserveBalance1;
    }

    /**
     * @dev calculates the accumulated network fee and transfers it to the network fee wallet
     *
     * @param _value amount of ether to exclude from the ether reserve balance (if relevant)
     *
     * @return new reserve balances
     */
    function processNetworkFees(uint256 _value) internal returns (uint256, uint256) {
        syncReserveBalances(_value);
        (uint256 reserveBalance0, uint256 reserveBalance1) = reserveBalances(1, 2);
        (ITokenHolder wallet, uint256 fee0, uint256 fee1) = networkWalletAndFees(reserveBalance0, reserveBalance1);
        reserveBalance0 -= fee0;
        reserveBalance1 -= fee1;
        setReserveBalances(1, 2, reserveBalance0, reserveBalance1);
        safeTransfer(__reserveTokens[0], address(wallet), fee0);
        safeTransfer(__reserveTokens[1], address(wallet), fee1);
        return (reserveBalance0, reserveBalance1);
    }

    /**
     * @dev returns the reserve balances of the given reserve tokens minus their corresponding fees
     *
     * @param _reserveTokens reserve tokens
     *
     * @return reserve balances minus their corresponding fees
     */
    function baseReserveBalances(IERC20[] memory _reserveTokens) internal view returns (uint256[2] memory) {
        uint256 reserveId0 = __reserveIds[_reserveTokens[0]];
        uint256 reserveId1 = __reserveIds[_reserveTokens[1]];
        (uint256 reserveBalance0, uint256 reserveBalance1) = reserveBalances(reserveId0, reserveId1);
        (, uint256 fee0, uint256 fee1) = networkWalletAndFees(reserveBalance0, reserveBalance1);
        return [reserveBalance0 - fee0, reserveBalance1 - fee1];
    }

    /**
     * @dev converts a specific amount of source tokens to target tokens
     * can only be called by the bancor network contract
     *
     * @param _sourceToken source ERC20 token
     * @param _targetToken target ERC20 token
     * @param _amount      amount of tokens to convert (in units of the source token)
     * @param _trader      address of the caller who executed the conversion
     * @param _beneficiary wallet to receive the conversion result
     *
     * @return amount of tokens received (in units of the target token)
     */
    function convert(
        IERC20 _sourceToken,
        IERC20 _targetToken,
        uint256 _amount,
        address _trader,
        address payable _beneficiary
    ) public payable override protected only(BANCOR_NETWORK) returns (uint256) {
        // validate input
        require(_sourceToken != _targetToken, "ERR_SAME_SOURCE_TARGET");

        return doConvert(_sourceToken, _targetToken, _amount, _trader, _beneficiary);
    }

    /**
     * @dev returns the conversion fee for a given target amount
     *
     * @param _targetAmount  target amount
     *
     * @return conversion fee
     */
    function calculateFee(uint256 _targetAmount) internal view returns (uint256) {
        return _targetAmount.mul(conversionFee) / PPM_RESOLUTION;
    }

    /**
     * @dev returns the conversion fee taken from a given target amount
     *
     * @param _targetAmount  target amount
     *
     * @return conversion fee
     */
    function calculateFeeInv(uint256 _targetAmount) internal view returns (uint256) {
        return _targetAmount.mul(conversionFee).div(PPM_RESOLUTION - conversionFee);
    }

    /**
     * @dev loads the stored reserve balance for a given reserve id
     *
     * @param _reserveId   reserve id
     */
    function reserveBalance(uint256 _reserveId) internal view returns (uint256) {
        return decodeReserveBalance(__reserveBalances, _reserveId);
    }

    /**
     * @dev loads the stored reserve balances
     *
     * @param _sourceId    source reserve id
     * @param _targetId    target reserve id
     */
    function reserveBalances(uint256 _sourceId, uint256 _targetId) internal view returns (uint256, uint256) {
        require((_sourceId == 1 && _targetId == 2) || (_sourceId == 2 && _targetId == 1), "ERR_INVALID_RESERVES");
        return decodeReserveBalances(__reserveBalances, _sourceId, _targetId);
    }

    /**
     * @dev stores the stored reserve balance for a given reserve id
     *
     * @param _reserveId       reserve id
     * @param _reserveBalance  reserve balance
     */
    function setReserveBalance(uint256 _reserveId, uint256 _reserveBalance) internal {
        require(_reserveBalance <= MAX_UINT128, "ERR_RESERVE_BALANCE_OVERFLOW");
        uint256 otherBalance = decodeReserveBalance(__reserveBalances, 3 - _reserveId);
        __reserveBalances = encodeReserveBalances(_reserveBalance, _reserveId, otherBalance, 3 - _reserveId);
    }

    /**
     * @dev stores the stored reserve balances
     *
     * @param _sourceId        source reserve id
     * @param _targetId        target reserve id
     * @param _sourceBalance   source reserve balance
     * @param _targetBalance   target reserve balance
     */
    function setReserveBalances(
        uint256 _sourceId,
        uint256 _targetId,
        uint256 _sourceBalance,
        uint256 _targetBalance
    ) internal {
        require(_sourceBalance <= MAX_UINT128 && _targetBalance <= MAX_UINT128, "ERR_RESERVE_BALANCE_OVERFLOW");
        __reserveBalances = encodeReserveBalances(_sourceBalance, _sourceId, _targetBalance, _targetId);
    }

    /**
     * @dev syncs the stored reserve balance for a given reserve with the real reserve balance
     *
     * @param _reserveToken    address of the reserve token
     */
    function syncReserveBalance(IERC20 _reserveToken) internal {
        uint256 reserveId = __reserveIds[_reserveToken];
        uint256 balance =
            _reserveToken == NATIVE_TOKEN_ADDRESS ? address(this).balance : _reserveToken.balanceOf(address(this));
        setReserveBalance(reserveId, balance);
    }

    /**
     * @dev syncs all stored reserve balances, excluding a given amount of ether from the ether reserve balance (if relevant)
     *
     * @param _value   amount of ether to exclude from the ether reserve balance (if relevant)
     */
    function syncReserveBalances(uint256 _value) internal {
        IERC20 _reserveToken0 = __reserveTokens[0];
        IERC20 _reserveToken1 = __reserveTokens[1];
        uint256 balance0 =
            _reserveToken0 == NATIVE_TOKEN_ADDRESS
                ? address(this).balance - _value
                : _reserveToken0.balanceOf(address(this));
        uint256 balance1 =
            _reserveToken1 == NATIVE_TOKEN_ADDRESS
                ? address(this).balance - _value
                : _reserveToken1.balanceOf(address(this));
        setReserveBalances(1, 2, balance0, balance1);
    }

    /**
     * @dev helper, dispatches the Conversion event
     *
     * @param _sourceToken     source ERC20 token
     * @param _targetToken     target ERC20 token
     * @param _trader          address of the caller who executed the conversion
     * @param _amount          amount purchased/sold (in the source token)
     * @param _returnAmount    amount returned (in the target token)
     */
    function dispatchConversionEvent(
        IERC20 _sourceToken,
        IERC20 _targetToken,
        address _trader,
        uint256 _amount,
        uint256 _returnAmount,
        uint256 _feeAmount
    ) internal {
        emit Conversion(_sourceToken, _targetToken, _trader, _amount, _returnAmount, int256(_feeAmount));
    }

    /**
     * @dev returns the expected amount and expected fee for converting one reserve to another
     *
     * @param _sourceToken address of the source reserve token contract
     * @param _targetToken address of the target reserve token contract
     * @param _amount      amount of source reserve tokens converted
     *
     * @return expected amount in units of the target reserve token
     * @return expected fee in units of the target reserve token
     */
    function targetAmountAndFee(
        IERC20 _sourceToken,
        IERC20 _targetToken,
        uint256 _amount
    ) public view virtual override active returns (uint256, uint256) {
        uint256 sourceId = __reserveIds[_sourceToken];
        uint256 targetId = __reserveIds[_targetToken];

        (uint256 sourceBalance, uint256 targetBalance) = reserveBalances(sourceId, targetId);

        return targetAmountAndFee(_sourceToken, _targetToken, sourceBalance, targetBalance, _amount);
    }

    /**
     * @dev returns the expected amount and expected fee for converting one reserve to another
     *
     * @param _sourceBalance    balance in the source reserve token contract
     * @param _targetBalance    balance in the target reserve token contract
     * @param _amount           amount of source reserve tokens converted
     *
     * @return expected amount in units of the target reserve token
     * @return expected fee in units of the target reserve token
     */
    function targetAmountAndFee(
        IERC20, /* _sourceToken */
        IERC20, /* _targetToken */
        uint256 _sourceBalance,
        uint256 _targetBalance,
        uint256 _amount
    ) internal view virtual returns (uint256, uint256) {
        uint256 amount = crossReserveTargetAmount(_sourceBalance, _targetBalance, _amount);

        uint256 fee = calculateFee(amount);

        return (amount - fee, fee);
    }

    /**
     * @dev returns the required amount and expected fee for converting one reserve to another
     *
     * @param _sourceToken address of the source reserve token contract
     * @param _targetToken address of the target reserve token contract
     * @param _amount      amount of target reserve tokens desired
     *
     * @return required amount in units of the source reserve token
     * @return expected fee in units of the target reserve token
     */
    function sourceAmountAndFee(
        IERC20 _sourceToken,
        IERC20 _targetToken,
        uint256 _amount
    ) public view virtual active returns (uint256, uint256) {
        uint256 sourceId = __reserveIds[_sourceToken];
        uint256 targetId = __reserveIds[_targetToken];

        (uint256 sourceBalance, uint256 targetBalance) = reserveBalances(sourceId, targetId);

        uint256 fee = calculateFeeInv(_amount);

        uint256 amount = crossReserveSourceAmount(sourceBalance, targetBalance, _amount.add(fee));

        return (amount, fee);
    }

    /**
     * @dev converts a specific amount of source tokens to target tokens
     *
     * @param _sourceToken source ERC20 token
     * @param _targetToken target ERC20 token
     * @param _amount      amount of tokens to convert (in units of the source token)
     * @param _trader      address of the caller who executed the conversion
     * @param _beneficiary wallet to receive the conversion result
     *
     * @return amount of tokens received (in units of the target token)
     */
    function doConvert(
        IERC20 _sourceToken,
        IERC20 _targetToken,
        uint256 _amount,
        address _trader,
        address payable _beneficiary
    ) internal returns (uint256) {
        // update the recent average rate
        updateRecentAverageRate();

        uint256 sourceId = __reserveIds[_sourceToken];
        uint256 targetId = __reserveIds[_targetToken];

        (uint256 sourceBalance, uint256 targetBalance) = reserveBalances(sourceId, targetId);

        // get the target amount minus the conversion fee and the conversion fee
        (uint256 amount, uint256 fee) =
            targetAmountAndFee(_sourceToken, _targetToken, sourceBalance, targetBalance, _amount);

        // ensure that the trade gives something in return
        require(amount != 0, "ERR_ZERO_TARGET_AMOUNT");

        // ensure that the trade won't deplete the reserve balance
        assert(amount < targetBalance);

        // ensure that the input amount was already deposited
        uint256 actualSourceBalance;
        if (_sourceToken == NATIVE_TOKEN_ADDRESS) {
            actualSourceBalance = address(this).balance;
            require(msg.value == _amount, "ERR_ETH_AMOUNT_MISMATCH");
        } else {
            actualSourceBalance = _sourceToken.balanceOf(address(this));
            require(msg.value == 0 && actualSourceBalance.sub(sourceBalance) >= _amount, "ERR_INVALID_AMOUNT");
        }

        // sync the reserve balances
        setReserveBalances(sourceId, targetId, actualSourceBalance, targetBalance - amount);

        // transfer funds to the beneficiary in the to reserve token
        safeTransfer(_targetToken, _beneficiary, amount);

        // dispatch the conversion event
        dispatchConversionEvent(_sourceToken, _targetToken, _trader, _amount, amount, fee);

        // dispatch rate updates
        dispatchTokenRateUpdateEvents(_sourceToken, _targetToken, actualSourceBalance, targetBalance - amount);

        return amount;
    }

    /**
     * @dev returns the recent average rate of 1 `_token` in the other reserve token units
     *
     * @param _token   token to get the rate for
     *
     * @return recent average rate between the reserves (numerator)
     * @return recent average rate between the reserves (denominator)
     */
    function recentAverageRate(IERC20 _token) external view validReserve(_token) returns (uint256, uint256) {
        // get the recent average rate of reserve 0
        uint256 rate = calcRecentAverageRate(averageRateInfo);

        uint256 rateN = decodeAverageRateN(rate);
        uint256 rateD = decodeAverageRateD(rate);

        if (_token == __reserveTokens[0]) {
            return (rateN, rateD);
        }

        return (rateD, rateN);
    }

    /**
     * @dev updates the recent average rate if needed
     */
    function updateRecentAverageRate() internal {
        uint256 averageRateInfo1 = averageRateInfo;
        uint256 averageRateInfo2 = calcRecentAverageRate(averageRateInfo1);
        if (averageRateInfo1 != averageRateInfo2) {
            averageRateInfo = averageRateInfo2;
        }
    }

    /**
     * @dev returns the recent average rate of 1 reserve token 0 in reserve token 1 units
     *
     * @param _averageRateInfo a local copy of the `averageRateInfo` state-variable
     *
     * @return recent average rate between the reserves
     */
    function calcRecentAverageRate(uint256 _averageRateInfo) internal view returns (uint256) {
        // get the previous average rate and its update-time
        uint256 prevAverageRateT = decodeAverageRateT(_averageRateInfo);
        uint256 prevAverageRateN = decodeAverageRateN(_averageRateInfo);
        uint256 prevAverageRateD = decodeAverageRateD(_averageRateInfo);

        // get the elapsed time since the previous average rate was calculated
        uint256 currentTime = time();
        uint256 timeElapsed = currentTime - prevAverageRateT;

        // if the previous average rate was calculated in the current block, the average rate remains unchanged
        if (timeElapsed == 0) {
            return _averageRateInfo;
        }

        // get the current rate between the reserves
        (uint256 currentRateD, uint256 currentRateN) = reserveBalances();

        // if the previous average rate was calculated a while ago or never, the average rate is equal to the current rate
        if (timeElapsed >= AVERAGE_RATE_PERIOD || prevAverageRateT == 0) {
            (currentRateN, currentRateD) = MathEx.reducedRatio(currentRateN, currentRateD, MAX_UINT112);
            return encodeAverageRateInfo(currentTime, currentRateN, currentRateD);
        }

        uint256 x = prevAverageRateD.mul(currentRateN);
        uint256 y = prevAverageRateN.mul(currentRateD);

        // since we know that timeElapsed < AVERAGE_RATE_PERIOD, we can avoid using SafeMath:
        uint256 newRateN = y.mul(AVERAGE_RATE_PERIOD - timeElapsed).add(x.mul(timeElapsed));
        uint256 newRateD = prevAverageRateD.mul(currentRateD).mul(AVERAGE_RATE_PERIOD);

        (newRateN, newRateD) = MathEx.reducedRatio(newRateN, newRateD, MAX_UINT112);
        return encodeAverageRateInfo(currentTime, newRateN, newRateD);
    }

    /**
     * @dev increases the pool's liquidity and mints new shares in the pool to the caller
     *
     * @param _reserveTokens   address of each reserve token
     * @param _reserveAmounts  amount of each reserve token
     * @param _minReturn       token minimum return-amount
     *
     * @return amount of pool tokens issued
     */
    function addLiquidity(
        IERC20[] memory _reserveTokens,
        uint256[] memory _reserveAmounts,
        uint256 _minReturn
    ) public payable protected active returns (uint256) {
        // verify the user input
        verifyLiquidityInput(_reserveTokens, _reserveAmounts, _minReturn);

        // if one of the reserves is ETH, then verify that the input amount of ETH is equal to the input value of ETH
        for (uint256 i = 0; i < 2; i++) {
            if (_reserveTokens[i] == NATIVE_TOKEN_ADDRESS) {
                require(_reserveAmounts[i] == msg.value, "ERR_ETH_AMOUNT_MISMATCH");
            }
        }

        // if the input value of ETH is larger than zero, then verify that one of the reserves is ETH
        if (msg.value > 0) {
            require(__reserveIds[NATIVE_TOKEN_ADDRESS] != 0, "ERR_NO_ETH_RESERVE");
        }

        // save a local copy of the pool token
        IDSToken poolToken = IDSToken(address(anchor));

        // get the total supply
        uint256 totalSupply = poolToken.totalSupply();

        uint256[2] memory prevReserveBalances;
        uint256[2] memory newReserveBalances;

        // process the network fees and get the reserve balances
        (prevReserveBalances[0], prevReserveBalances[1]) = processNetworkFees(msg.value);

        uint256 amount;
        uint256[2] memory reserveAmounts;

        // calculate the amount of pool tokens to mint for the caller
        // and the amount of reserve tokens to transfer from the caller
        if (totalSupply == 0) {
            amount = MathEx.geometricMean(_reserveAmounts);
            reserveAmounts[0] = _reserveAmounts[0];
            reserveAmounts[1] = _reserveAmounts[1];
        } else {
            (amount, reserveAmounts) = addLiquidityAmounts(
                _reserveTokens,
                _reserveAmounts,
                prevReserveBalances,
                totalSupply
            );
        }

        uint256 newPoolTokenSupply = totalSupply.add(amount);
        for (uint256 i = 0; i < 2; i++) {
            IERC20 reserveToken = _reserveTokens[i];
            uint256 reserveAmount = reserveAmounts[i];
            require(reserveAmount > 0, "ERR_ZERO_TARGET_AMOUNT");
            assert(reserveAmount <= _reserveAmounts[i]);

            // transfer each one of the reserve amounts from the user to the pool
            if (reserveToken != NATIVE_TOKEN_ADDRESS) {
                // ETH has already been transferred as part of the transaction
                reserveToken.safeTransferFrom(msg.sender, address(this), reserveAmount);
            } else if (_reserveAmounts[i] > reserveAmount) {
                // transfer the extra amount of ETH back to the user
                msg.sender.transfer(_reserveAmounts[i] - reserveAmount);
            }

            // save the new reserve balance
            newReserveBalances[i] = prevReserveBalances[i].add(reserveAmount);

            emit LiquidityAdded(msg.sender, reserveToken, reserveAmount, newReserveBalances[i], newPoolTokenSupply);

            // dispatch the `TokenRateUpdate` event for the pool token
            emit TokenRateUpdate(poolToken, reserveToken, newReserveBalances[i], newPoolTokenSupply);
        }

        // set the reserve balances
        setReserveBalances(1, 2, newReserveBalances[0], newReserveBalances[1]);

        // set the reserve balances product
        _reserveBalancesProduct = newReserveBalances[0] * newReserveBalances[1];

        // verify that the equivalent amount of tokens is equal to or larger than the user's expectation
        require(amount >= _minReturn, "ERR_RETURN_TOO_LOW");

        // issue the tokens to the user
        poolToken.issue(msg.sender, amount);

        // return the amount of pool tokens issued
        return amount;
    }

    /**
     * @dev get the amount of pool tokens to mint for the caller
     * and the amount of reserve tokens to transfer from the caller
     *
     * @param _reserveAmounts   amount of each reserve token
     * @param _reserveBalances  balance of each reserve token
     * @param _totalSupply      total supply of pool tokens
     *
     * @return amount of pool tokens to mint for the caller
     * @return amount of reserve tokens to transfer from the caller
     */
    function addLiquidityAmounts(
        IERC20[] memory, /* _reserveTokens */
        uint256[] memory _reserveAmounts,
        uint256[2] memory _reserveBalances,
        uint256 _totalSupply
    ) internal view virtual returns (uint256, uint256[2] memory) {
        this;

        uint256 index =
            _reserveAmounts[0].mul(_reserveBalances[1]) < _reserveAmounts[1].mul(_reserveBalances[0]) ? 0 : 1;
        uint256 amount = fundSupplyAmount(_totalSupply, _reserveBalances[index], _reserveAmounts[index]);

        uint256[2] memory reserveAmounts =
            [fundCost(_totalSupply, _reserveBalances[0], amount), fundCost(_totalSupply, _reserveBalances[1], amount)];

        return (amount, reserveAmounts);
    }

    /**
     * @dev decreases the pool's liquidity and burns the caller's shares in the pool
     *
     * @param _amount                  token amount
     * @param _reserveTokens           address of each reserve token
     * @param _reserveMinReturnAmounts minimum return-amount of each reserve token
     *
     * @return the amount of each reserve token granted for the given amount of pool tokens
     */
    function removeLiquidity(
        uint256 _amount,
        IERC20[] memory _reserveTokens,
        uint256[] memory _reserveMinReturnAmounts
    ) public protected active returns (uint256[] memory) {
        // verify the user input
        bool inputRearranged = verifyLiquidityInput(_reserveTokens, _reserveMinReturnAmounts, _amount);

        // save a local copy of the pool token
        IDSToken poolToken = IDSToken(address(anchor));

        // get the total supply BEFORE destroying the user tokens
        uint256 totalSupply = poolToken.totalSupply();

        // destroy the user tokens
        poolToken.destroy(msg.sender, _amount);

        uint256 newPoolTokenSupply = totalSupply.sub(_amount);

        uint256[2] memory prevReserveBalances;
        uint256[2] memory newReserveBalances;

        // process the network fees and get the reserve balances
        (prevReserveBalances[0], prevReserveBalances[1]) = processNetworkFees(0);

        uint256[] memory reserveAmounts = removeLiquidityReserveAmounts(_amount, totalSupply, prevReserveBalances);

        for (uint256 i = 0; i < 2; i++) {
            IERC20 reserveToken = _reserveTokens[i];
            uint256 reserveAmount = reserveAmounts[i];
            require(reserveAmount >= _reserveMinReturnAmounts[i], "ERR_ZERO_TARGET_AMOUNT");

            // save the new reserve balance
            newReserveBalances[i] = prevReserveBalances[i].sub(reserveAmount);

            // transfer each one of the reserve amounts from the pool to the user
            safeTransfer(reserveToken, msg.sender, reserveAmount);

            emit LiquidityRemoved(msg.sender, reserveToken, reserveAmount, newReserveBalances[i], newPoolTokenSupply);

            // dispatch the `TokenRateUpdate` event for the pool token
            emit TokenRateUpdate(poolToken, reserveToken, newReserveBalances[i], newPoolTokenSupply);
        }

        // set the reserve balances
        setReserveBalances(1, 2, newReserveBalances[0], newReserveBalances[1]);

        // set the reserve balances product
        _reserveBalancesProduct = newReserveBalances[0] * newReserveBalances[1];

        if (inputRearranged) {
            uint256 tempReserveAmount = reserveAmounts[0];
            reserveAmounts[0] = reserveAmounts[1];
            reserveAmounts[1] = tempReserveAmount;
        }

        // return the amount of each reserve token granted for the given amount of pool tokens
        return reserveAmounts;
    }

    /**
     * @dev given the amount of one of the reserve tokens to add liquidity of,
     * returns the required amount of each one of the other reserve tokens
     * since an empty pool can be funded with any list of non-zero input amounts,
     * this function assumes that the pool is not empty (has already been funded)
     *
     * @param _reserveTokens       address of each reserve token
     * @param _reserveTokenIndex   index of the relevant reserve token
     * @param _reserveAmount       amount of the relevant reserve token
     *
     * @return the required amount of each one of the reserve tokens
     */
    function addLiquidityCost(
        IERC20[] memory _reserveTokens,
        uint256 _reserveTokenIndex,
        uint256 _reserveAmount
    ) public view returns (uint256[] memory) {
        uint256 totalSupply = IDSToken(address(anchor)).totalSupply();
        uint256[2] memory baseBalances = baseReserveBalances(_reserveTokens);
        uint256 amount = fundSupplyAmount(totalSupply, baseBalances[_reserveTokenIndex], _reserveAmount);

        uint256[] memory reserveAmounts = new uint256[](2);
        reserveAmounts[0] = fundCost(totalSupply, baseBalances[0], amount);
        reserveAmounts[1] = fundCost(totalSupply, baseBalances[1], amount);
        return reserveAmounts;
    }

    /**
     * @dev returns the amount of pool tokens entitled for given amounts of reserve tokens
     * since an empty pool can be funded with any list of non-zero input amounts,
     * this function assumes that the pool is not empty (has already been funded)
     *
     * @param _reserveTokens   address of each reserve token
     * @param _reserveAmounts  amount of each reserve token
     *
     * @return the amount of pool tokens entitled for the given amounts of reserve tokens
     */
    function addLiquidityReturn(IERC20[] memory _reserveTokens, uint256[] memory _reserveAmounts)
        public
        view
        returns (uint256)
    {
        uint256 totalSupply = IDSToken(address(anchor)).totalSupply();
        uint256[2] memory baseBalances = baseReserveBalances(_reserveTokens);
        (uint256 amount, ) = addLiquidityAmounts(_reserveTokens, _reserveAmounts, baseBalances, totalSupply);
        return amount;
    }

    /**
     * @dev returns the amount of each reserve token entitled for a given amount of pool tokens
     *
     * @param _amount          amount of pool tokens
     * @param _reserveTokens   address of each reserve token
     *
     * @return the amount of each reserve token entitled for the given amount of pool tokens
     */
    function removeLiquidityReturn(uint256 _amount, IERC20[] memory _reserveTokens)
        public
        view
        returns (uint256[] memory)
    {
        uint256 totalSupply = IDSToken(address(anchor)).totalSupply();
        uint256[2] memory baseBalances = baseReserveBalances(_reserveTokens);
        return removeLiquidityReserveAmounts(_amount, totalSupply, baseBalances);
    }

    /**
     * @dev verifies that a given array of tokens is identical to the converter's array of reserve tokens
     * we take this input in order to allow specifying the corresponding reserve amounts in any order
     * this function rearranges the input arrays according to the converter's array of reserve tokens
     *
     * @param _reserveTokens   array of reserve tokens
     * @param _reserveAmounts  array of reserve amounts
     * @param _amount          token amount
     *
     * @return true if the function has rearranged the input arrays; false otherwise
     */
    function verifyLiquidityInput(
        IERC20[] memory _reserveTokens,
        uint256[] memory _reserveAmounts,
        uint256 _amount
    ) private view returns (bool) {
        require(validReserveAmounts(_reserveAmounts) && _amount > 0, "ERR_ZERO_AMOUNT");

        uint256 reserve0Id = __reserveIds[_reserveTokens[0]];
        uint256 reserve1Id = __reserveIds[_reserveTokens[1]];

        if (reserve0Id == 2 && reserve1Id == 1) {
            IERC20 tempReserveToken = _reserveTokens[0];
            _reserveTokens[0] = _reserveTokens[1];
            _reserveTokens[1] = tempReserveToken;
            uint256 tempReserveAmount = _reserveAmounts[0];
            _reserveAmounts[0] = _reserveAmounts[1];
            _reserveAmounts[1] = tempReserveAmount;
            return true;
        }

        require(reserve0Id == 1 && reserve1Id == 2, "ERR_INVALID_RESERVE");
        return false;
    }

    /**
     * @dev checks whether or not both reserve amounts are larger than zero
     *
     * @param _reserveAmounts  array of reserve amounts
     *
     * @return true if both reserve amounts are larger than zero; false otherwise
     */
    function validReserveAmounts(uint256[] memory _reserveAmounts) internal pure virtual returns (bool) {
        return _reserveAmounts[0] > 0 && _reserveAmounts[1] > 0;
    }

    /**
     * @dev returns the amount of each reserve token entitled for a given amount of pool tokens
     *
     * @param _amount          amount of pool tokens
     * @param _totalSupply     total supply of pool tokens
     * @param _reserveBalances balance of each reserve token
     *
     * @return the amount of each reserve token entitled for the given amount of pool tokens
     */
    function removeLiquidityReserveAmounts(
        uint256 _amount,
        uint256 _totalSupply,
        uint256[2] memory _reserveBalances
    ) private pure returns (uint256[] memory) {
        uint256[] memory reserveAmounts = new uint256[](2);
        reserveAmounts[0] = liquidateReserveAmount(_totalSupply, _reserveBalances[0], _amount);
        reserveAmounts[1] = liquidateReserveAmount(_totalSupply, _reserveBalances[1], _amount);
        return reserveAmounts;
    }

    /**
     * @dev dispatches token rate update events for the reserve tokens and the pool token
     *
     * @param _sourceToken     address of the source reserve token
     * @param _targetToken     address of the target reserve token
     * @param _sourceBalance   balance of the source reserve token
     * @param _targetBalance   balance of the target reserve token
     */
    function dispatchTokenRateUpdateEvents(
        IERC20 _sourceToken,
        IERC20 _targetToken,
        uint256 _sourceBalance,
        uint256 _targetBalance
    ) private {
        // save a local copy of the pool token
        IDSToken poolToken = IDSToken(address(anchor));

        // get the total supply of pool tokens
        uint256 poolTokenSupply = poolToken.totalSupply();

        // dispatch token rate update event for the reserve tokens
        emit TokenRateUpdate(_sourceToken, _targetToken, _targetBalance, _sourceBalance);

        // dispatch token rate update events for the pool token
        emit TokenRateUpdate(poolToken, _sourceToken, _sourceBalance, poolTokenSupply);
        emit TokenRateUpdate(poolToken, _targetToken, _targetBalance, poolTokenSupply);
    }

    function encodeReserveBalance(uint256 _balance, uint256 _id) private pure returns (uint256) {
        assert(_balance <= MAX_UINT128 && (_id == 1 || _id == 2));
        return _balance << ((_id - 1) * 128);
    }

    function decodeReserveBalance(uint256 _balances, uint256 _id) private pure returns (uint256) {
        assert(_id == 1 || _id == 2);
        return (_balances >> ((_id - 1) * 128)) & MAX_UINT128;
    }

    function encodeReserveBalances(
        uint256 _balance0,
        uint256 _id0,
        uint256 _balance1,
        uint256 _id1
    ) private pure returns (uint256) {
        return encodeReserveBalance(_balance0, _id0) | encodeReserveBalance(_balance1, _id1);
    }

    function decodeReserveBalances(
        uint256 _balances,
        uint256 _id0,
        uint256 _id1
    ) private pure returns (uint256, uint256) {
        return (decodeReserveBalance(_balances, _id0), decodeReserveBalance(_balances, _id1));
    }

    function encodeAverageRateInfo(
        uint256 _averageRateT,
        uint256 _averageRateN,
        uint256 _averageRateD
    ) private pure returns (uint256) {
        assert(_averageRateT <= MAX_UINT32 && _averageRateN <= MAX_UINT112 && _averageRateD <= MAX_UINT112);
        return (_averageRateT << 224) | (_averageRateN << 112) | _averageRateD;
    }

    function decodeAverageRateT(uint256 _averageRateInfo) private pure returns (uint256) {
        return _averageRateInfo >> 224;
    }

    function decodeAverageRateN(uint256 _averageRateInfo) private pure returns (uint256) {
        return (_averageRateInfo >> 112) & MAX_UINT112;
    }

    function decodeAverageRateD(uint256 _averageRateInfo) private pure returns (uint256) {
        return _averageRateInfo & MAX_UINT112;
    }

    /**
     * @dev returns the largest integer smaller than or equal to the square root of a given value
     *
     * @param x the given value
     *
     * @return the largest integer smaller than or equal to the square root of the given value
     */
    function floorSqrt(uint256 x) private pure returns (uint256) {
        return x > 0 ? MathEx.floorSqrt(x) : 0;
    }

    function crossReserveTargetAmount(
        uint256 _sourceReserveBalance,
        uint256 _targetReserveBalance,
        uint256 _amount
    ) private pure returns (uint256) {
        // validate input
        require(_sourceReserveBalance > 0 && _targetReserveBalance > 0, "ERR_INVALID_RESERVE_BALANCE");

        return _targetReserveBalance.mul(_amount) / _sourceReserveBalance.add(_amount);
    }

    function crossReserveSourceAmount(
        uint256 _sourceReserveBalance,
        uint256 _targetReserveBalance,
        uint256 _amount
    ) private pure returns (uint256) {
        // validate input
        require(_sourceReserveBalance > 0, "ERR_INVALID_RESERVE_BALANCE");
        require(_amount < _targetReserveBalance, "ERR_INVALID_AMOUNT");

        if (_amount == 0) {
            return 0;
        }

        return (_sourceReserveBalance.mul(_amount) - 1) / (_targetReserveBalance - _amount) + 1;
    }

    function fundCost(
        uint256 _supply,
        uint256 _reserveBalance,
        uint256 _amount
    ) private pure returns (uint256) {
        // validate input
        require(_supply > 0, "ERR_INVALID_SUPPLY");
        require(_reserveBalance > 0, "ERR_INVALID_RESERVE_BALANCE");

        // special case for 0 amount
        if (_amount == 0) {
            return 0;
        }

        return (_amount.mul(_reserveBalance) - 1) / _supply + 1;
    }

    function fundSupplyAmount(
        uint256 _supply,
        uint256 _reserveBalance,
        uint256 _amount
    ) private pure returns (uint256) {
        // validate input
        require(_supply > 0, "ERR_INVALID_SUPPLY");
        require(_reserveBalance > 0, "ERR_INVALID_RESERVE_BALANCE");

        // special case for 0 amount
        if (_amount == 0) {
            return 0;
        }

        return _amount.mul(_supply) / _reserveBalance;
    }

    function liquidateReserveAmount(
        uint256 _supply,
        uint256 _reserveBalance,
        uint256 _amount
    ) private pure returns (uint256) {
        // validate input
        require(_supply > 0, "ERR_INVALID_SUPPLY");
        require(_reserveBalance > 0, "ERR_INVALID_RESERVE_BALANCE");
        require(_amount <= _supply, "ERR_INVALID_AMOUNT");

        // special case for 0 amount
        if (_amount == 0) {
            return 0;
        }

        // special case for liquidating the entire supply
        if (_amount == _supply) {
            return _reserveBalance;
        }

        return _amount.mul(_reserveBalance) / _supply;
    }

    /**
     * @dev returns the network wallet and fees
     *
     * @param reserveBalance0 1st reserve balance
     * @param reserveBalance1 2nd reserve balance
     *
     * @return the network wallet
     * @return the network fee on the 1st reserve
     * @return the network fee on the 2nd reserve
     */
    function networkWalletAndFees(uint256 reserveBalance0, uint256 reserveBalance1)
        private
        view
        returns (
            ITokenHolder,
            uint256,
            uint256
        )
    {
        uint256 prevPoint = floorSqrt(_reserveBalancesProduct);
        uint256 currPoint = floorSqrt(reserveBalance0 * reserveBalance1);

        if (prevPoint >= currPoint) {
            return (ITokenHolder(address(0)), 0, 0);
        }

        (ITokenHolder networkFeeWallet, uint32 networkFee) =
            INetworkSettings(addressOf(NETWORK_SETTINGS)).networkFeeParams();
        uint256 n = (currPoint - prevPoint) * networkFee;
        uint256 d = currPoint * PPM_RESOLUTION;
        return (networkFeeWallet, reserveBalance0.mul(n).div(d), reserveBalance1.mul(n).div(d));
    }

    /**
     * @dev transfers funds held by the contract and sends them to an account
     *
     * @param token ERC20 token contract address
     * @param to account to receive the new amount
     * @param amount amount to withdraw
     */
    function safeTransfer(
        IERC20 token,
        address to,
        uint256 amount
    ) private {
        if (amount == 0) {
            return;
        }

        if (token == NATIVE_TOKEN_ADDRESS) {
            payable(to).transfer(amount);
        } else {
            token.safeTransfer(to, amount);
        }
    }

    /**
     * @dev deprecated since version 28, backward compatibility - use only for earlier versions
     */
    function token() public view override returns (IConverterAnchor) {
        return anchor;
    }

    /**
     * @dev deprecated, backward compatibility
     */
    function transferTokenOwnership(address _newOwner) public override ownerOnly {
        transferAnchorOwnership(_newOwner);
    }

    /**
     * @dev deprecated, backward compatibility
     */
    function acceptTokenOwnership() public override ownerOnly {
        acceptAnchorOwnership();
    }

    /**
     * @dev deprecated, backward compatibility
     */
    function connectors(IERC20 _address)
        public
        view
        override
        returns (
            uint256,
            uint32,
            bool,
            bool,
            bool
        )
    {
        uint256 reserveId = __reserveIds[_address];
        if (reserveId != 0) {
            return (reserveBalance(reserveId), PPM_RESOLUTION / 2, false, false, true);
        }
        return (0, 0, false, false, false);
    }

    /**
     * @dev deprecated, backward compatibility
     */
    function connectorTokens(uint256 _index) public view override returns (IERC20) {
        return __reserveTokens[_index];
    }

    /**
     * @dev deprecated, backward compatibility
     */
    function connectorTokenCount() public view override returns (uint16) {
        return reserveTokenCount();
    }

    /**
     * @dev deprecated, backward compatibility
     */
    function getConnectorBalance(IERC20 _connectorToken) public view override returns (uint256) {
        return reserveBalance(_connectorToken);
    }

    /**
     * @dev deprecated, backward compatibility
     */
    function getReturn(
        IERC20 _sourceToken,
        IERC20 _targetToken,
        uint256 _amount
    ) public view returns (uint256, uint256) {
        return targetAmountAndFee(_sourceToken, _targetToken, _amount);
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
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);
}

// File: @openzeppelin/contracts/math/SafeMath.sol



pragma solidity >=0.6.0 <0.8.0;

/**
 * @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, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin/contracts/utils/Address.sol



pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/SafeERC20.sol



pragma solidity >=0.6.0 <0.8.0;




/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: solidity/contracts/utility/interfaces/IOwned.sol


pragma solidity 0.6.12;

/*
    Owned contract interface
*/
interface IOwned {
    // this function isn't since the compiler emits automatically generated getter functions as external
    function owner() external view returns (address);

    function transferOwnership(address _newOwner) external;

    function acceptOwnership() external;
}

// File: solidity/contracts/utility/Owned.sol


pragma solidity 0.6.12;


/**
 * @dev This contract provides support and utilities for contract ownership.
 */
contract Owned is IOwned {
    address public override owner;
    address public newOwner;

    /**
     * @dev triggered when the owner is updated
     *
     * @param _prevOwner previous owner
     * @param _newOwner  new owner
     */
    event OwnerUpdate(address indexed _prevOwner, address indexed _newOwner);

    /**
     * @dev initializes a new Owned instance
     */
    constructor() public {
        owner = msg.sender;
    }

    // allows execution by the owner only
    modifier ownerOnly {
        _ownerOnly();
        _;
    }

    // error message binary size optimization
    function _ownerOnly() internal view {
        require(msg.sender == owner, "ERR_ACCESS_DENIED");
    }

    /**
     * @dev allows transferring the contract ownership
     * the new owner still needs to accept the transfer
     * can only be called by the contract owner
     *
     * @param _newOwner    new contract owner
     */
    function transferOwnership(address _newOwner) public override ownerOnly {
        require(_newOwner != owner, "ERR_SAME_OWNER");
        newOwner = _newOwner;
    }

    /**
     * @dev used by a new owner to accept an ownership transfer
     */
    function acceptOwnership() public override {
        require(msg.sender == newOwner, "ERR_ACCESS_DENIED");
        emit OwnerUpdate(owner, newOwner);
        owner = newOwner;
        newOwner = address(0);
    }
}

// File: solidity/contracts/utility/Utils.sol


pragma solidity 0.6.12;


/**
 * @dev Utilities & Common Modifiers
 */
contract Utils {
    uint32 internal constant PPM_RESOLUTION = 1000000;
    IERC20 internal constant NATIVE_TOKEN_ADDRESS = IERC20(0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE);

    // verifies that a value is greater than zero
    modifier greaterThanZero(uint256 _value) {
        _greaterThanZero(_value);
        _;
    }

    // error message binary size optimization
    function _greaterThanZero(uint256 _value) internal pure {
        require(_value > 0, "ERR_ZERO_VALUE");
    }

    // validates an address - currently only checks that it isn't null
    modifier validAddress(address _address) {
        _validAddress(_address);
        _;
    }

    // error message binary size optimization
    function _validAddress(address _address) internal pure {
        require(_address != address(0), "ERR_INVALID_ADDRESS");
    }

    // ensures that the portion is valid
    modifier validPortion(uint32 _portion) {
        _validPortion(_portion);
        _;
    }

    // error message binary size optimization
    function _validPortion(uint32 _portion) internal pure {
        require(_portion > 0 && _portion <= PPM_RESOLUTION, "ERR_INVALID_PORTION");
    }

    // validates an external address - currently only checks that it isn't null or this
    modifier validExternalAddress(address _address) {
        _validExternalAddress(_address);
        _;
    }

    // error message binary size optimization
    function _validExternalAddress(address _address) internal view {
        require(_address != address(0) && _address != address(this), "ERR_INVALID_EXTERNAL_ADDRESS");
    }

    // ensures that the fee is valid
    modifier validFee(uint32 fee) {
        _validFee(fee);
        _;
    }

    // error message binary size optimization
    function _validFee(uint32 fee) internal pure {
        require(fee <= PPM_RESOLUTION, "ERR_INVALID_FEE");
    }
}

// File: solidity/contracts/utility/interfaces/ITokenHolder.sol


pragma solidity 0.6.12;



/*
    Token Holder interface
*/
interface ITokenHolder is IOwned {
    receive() external payable;

    function withdrawTokens(
        IERC20 token,
        address payable to,
        uint256 amount
    ) external;

    function withdrawTokensMultiple(
        IERC20[] calldata tokens,
        address payable to,
        uint256[] calldata amounts
    ) external;
}

// File: solidity/contracts/utility/TokenHolder.sol


pragma solidity 0.6.12;





/**
 * @dev This contract provides a safety mechanism for allowing the owner to
 * send tokens that were sent to the contract by mistake back to the sender.
 *
 * We consider every contract to be a 'token holder' since it's currently not possible
 * for a contract to deny receiving tokens.
 */
contract TokenHolder is ITokenHolder, Owned, Utils {
    using SafeERC20 for IERC20;

    // prettier-ignore
    receive() external payable override virtual {}

    /**
     * @dev withdraws funds held by the contract and sends them to an account
     * can only be called by the owner
     *
     * @param token ERC20 token contract address (with a special handling of NATIVE_TOKEN_ADDRESS)
     * @param to account to receive the new amount
     * @param amount amount to withdraw
     */
    function withdrawTokens(
        IERC20 token,
        address payable to,
        uint256 amount
    ) public virtual override ownerOnly validAddress(to) {
        safeTransfer(token, to, amount);
    }

    /**
     * @dev withdraws multiple funds held by the contract and sends them to an account
     * can only be called by the owner
     *
     * @param tokens ERC20 token contract addresses (with a special handling of NATIVE_TOKEN_ADDRESS)
     * @param to account to receive the new amount
     * @param amounts amounts to withdraw
     */
    function withdrawTokensMultiple(
        IERC20[] calldata tokens,
        address payable to,
        uint256[] calldata amounts
    ) public virtual override ownerOnly validAddress(to) {
        uint256 length = tokens.length;
        require(length == amounts.length, "ERR_INVALID_LENGTH");

        for (uint256 i = 0; i < length; ++i) {
            safeTransfer(tokens[i], to, amounts[i]);
        }
    }

    /**
     * @dev transfers funds held by the contract and sends them to an account
     *
     * @param token ERC20 token contract address
     * @param to account to receive the new amount
     * @param amount amount to withdraw
     */
    function safeTransfer(
        IERC20 token,
        address payable to,
        uint256 amount
    ) internal {
        if (amount == 0) {
            return;
        }

        if (token == NATIVE_TOKEN_ADDRESS) {
            to.transfer(amount);
        } else {
            token.safeTransfer(to, amount);
        }
    }
}

pragma solidity ^0.4.11;

/*
    Overflow protected math functions
*/
contract SafeMath {
    /**
        constructor
    */
    function SafeMath() {
    }

    /**
        @dev returns the sum of _x and _y, asserts if the calculation overflows

        @param _x   value 1
        @param _y   value 2

        @return sum
    */
    function safeAdd(uint256 _x, uint256 _y) internal returns (uint256) {
        uint256 z = _x + _y;
        assert(z >= _x);
        return z;
    }

    /**
        @dev returns the difference of _x minus _y, asserts if the subtraction results in a negative number

        @param _x   minuend
        @param _y   subtrahend

        @return difference
    */
    function safeSub(uint256 _x, uint256 _y) internal returns (uint256) {
        assert(_x >= _y);
        return _x - _y;
    }

    /**
        @dev returns the product of multiplying _x by _y, asserts if the calculation overflows

        @param _x   factor 1
        @param _y   factor 2

        @return product
    */
    function safeMul(uint256 _x, uint256 _y) internal returns (uint256) {
        uint256 z = _x * _y;
        assert(_x == 0 || z / _x == _y);
        return z;
    }
} 

/*
    Owned contract interface
*/
contract IOwned {
    // this function isn't abstract since the compiler emits automatically generated getter functions as external
    function owner() public constant returns (address owner) { owner; }

    function transferOwnership(address _newOwner) public;
    function acceptOwnership() public;
}

/*
    Provides support and utilities for contract ownership
*/
contract Owned is IOwned {
    address public owner;
    address public newOwner;

    event OwnerUpdate(address _prevOwner, address _newOwner);

    /**
        @dev constructor
    */
    function Owned() {
        owner = msg.sender;
    }

    // allows execution by the owner only
    modifier ownerOnly {
        assert(msg.sender == owner);
        _;
    }

    /**
        @dev allows transferring the contract ownership
        the new owner still need to accept the transfer
        can only be called by the contract owner

        @param _newOwner    new contract owner
    */
    function transferOwnership(address _newOwner) public ownerOnly {
        require(_newOwner != owner);
        newOwner = _newOwner;
    }

    /**
        @dev used by a new owner to accept an ownership transfer
    */
    function acceptOwnership() public {
        require(msg.sender == newOwner);
        OwnerUpdate(owner, newOwner);
        owner = newOwner;
        newOwner = 0x0;
    }
}

/*
    Token Holder interface
*/
contract ITokenHolder is IOwned {
    function withdrawTokens(IERC20Token _token, address _to, uint256 _amount) public;
}

/*
    We consider every contract to be a 'token holder' since it's currently not possible
    for a contract to deny receiving tokens.

    The TokenHolder's contract sole purpose is to provide a safety mechanism that allows
    the owner to send tokens that were sent to the contract by mistake back to their sender.
*/
contract TokenHolder is ITokenHolder, Owned {
    /**
        @dev constructor
    */
    function TokenHolder() {
    }

    // validates an address - currently only checks that it isn't null
    modifier validAddress(address _address) {
        require(_address != 0x0);
        _;
    }

    // verifies that the address is different than this contract address
    modifier notThis(address _address) {
        require(_address != address(this));
        _;
    }

    /**
        @dev withdraws tokens held by the contract and sends them to an account
        can only be called by the owner

        @param _token   ERC20 token contract address
        @param _to      account to receive the new amount
        @param _amount  amount to withdraw
    */
    function withdrawTokens(IERC20Token _token, address _to, uint256 _amount)
        public
        ownerOnly
        validAddress(_token)
        validAddress(_to)
        notThis(_to)
    {
        assert(_token.transfer(_to, _amount));
    }
}

/*
    ERC20 Standard Token interface
*/
contract IERC20Token {
    // these functions aren't abstract since the compiler emits automatically generated getter functions as external
    function name() public constant returns (string name) { name; }
    function symbol() public constant returns (string symbol) { symbol; }
    function decimals() public constant returns (uint8 decimals) { decimals; }
    function totalSupply() public constant returns (uint256 totalSupply) { totalSupply; }
    function balanceOf(address _owner) public constant returns (uint256 balance) { _owner; balance; }
    function allowance(address _owner, address _spender) public constant returns (uint256 remaining) { _owner; _spender; remaining; }

    function transfer(address _to, uint256 _value) public returns (bool success);
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);
    function approve(address _spender, uint256 _value) public returns (bool success);
}

/**
    ERC20 Standard Token implementation
*/
contract ERC20Token is IERC20Token, SafeMath {
    string public standard = 'Token 0.1';
    string public name = '';
    string public symbol = '';
    uint8 public decimals = 0;
    uint256 public totalSupply = 0;
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

    /**
        @dev constructor

        @param _name        token name
        @param _symbol      token symbol
        @param _decimals    decimal points, for display purposes
    */
    function ERC20Token(string _name, string _symbol, uint8 _decimals) {
        require(bytes(_name).length > 0 && bytes(_symbol).length > 0); // validate input

        name = _name;
        symbol = _symbol;
        decimals = _decimals;
    }

    // validates an address - currently only checks that it isn't null
    modifier validAddress(address _address) {
        require(_address != 0x0);
        _;
    }

    /**
        @dev send coins
        throws on any error rather then return a false flag to minimize user errors

        @param _to      target address
        @param _value   transfer amount

        @return true if the transfer was successful, false if it wasn't
    */
    function transfer(address _to, uint256 _value)
        public
        validAddress(_to)
        returns (bool success)
    {
        balanceOf[msg.sender] = safeSub(balanceOf[msg.sender], _value);
        balanceOf[_to] = safeAdd(balanceOf[_to], _value);
        Transfer(msg.sender, _to, _value);
        return true;
    }

    /**
        @dev an account/contract attempts to get the coins
        throws on any error rather then return a false flag to minimize user errors

        @param _from    source address
        @param _to      target address
        @param _value   transfer amount

        @return true if the transfer was successful, false if it wasn't
    */
    function transferFrom(address _from, address _to, uint256 _value)
        public
        validAddress(_from)
        validAddress(_to)
        returns (bool success)
    {
        allowance[_from][msg.sender] = safeSub(allowance[_from][msg.sender], _value);
        balanceOf[_from] = safeSub(balanceOf[_from], _value);
        balanceOf[_to] = safeAdd(balanceOf[_to], _value);
        Transfer(_from, _to, _value);
        return true;
    }

    /**
        @dev allow another account/contract to spend some tokens on your behalf
        throws on any error rather then return a false flag to minimize user errors

        also, to minimize the risk of the approve/transferFrom attack vector
        (see https://docs.google.com/document/d/1YLPtQxZu1UAvO9cZ1O2RPXBbT0mooh4DYKjA_jp-RLM/), approve has to be called twice
        in 2 separate transactions - once to change the allowance to 0 and secondly to change it to the new allowance value

        @param _spender approved address
        @param _value   allowance amount

        @return true if the approval was successful, false if it wasn't
    */
    function approve(address _spender, uint256 _value)
        public
        validAddress(_spender)
        returns (bool success)
    {
        // if the allowance isn't 0, it can only be updated to 0 to prevent an allowance change immediately after withdrawal
        require(_value == 0 || allowance[msg.sender][_spender] == 0);

        allowance[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }
}

/*
    Smart Token interface
*/
contract ISmartToken is ITokenHolder, IERC20Token {
    function disableTransfers(bool _disable) public;
    function issue(address _to, uint256 _amount) public;
    function destroy(address _from, uint256 _amount) public;
}

/*
    Smart Token v0.2

    'Owned' is specified here for readability reasons
*/
contract SmartToken is ISmartToken, ERC20Token, Owned, TokenHolder {
    string public version = '0.2';

    bool public transfersEnabled = true;    // true if transfer/transferFrom are enabled, false if not

    // triggered when a smart token is deployed - the _token address is defined for forward compatibility, in case we want to trigger the event from a factory
    event NewSmartToken(address _token);
    // triggered when the total supply is increased
    event Issuance(uint256 _amount);
    // triggered when the total supply is decreased
    event Destruction(uint256 _amount);

    /**
        @dev constructor

        @param _name       token name
        @param _symbol     token short symbol, 1-6 characters
        @param _decimals   for display purposes only
    */
    function SmartToken(string _name, string _symbol, uint8 _decimals)
        ERC20Token(_name, _symbol, _decimals)
    {
        require(bytes(_symbol).length <= 6); // validate input
        NewSmartToken(address(this));
    }

    // allows execution only when transfers aren't disabled
    modifier transfersAllowed {
        assert(transfersEnabled);
        _;
    }

    /**
        @dev disables/enables transfers
        can only be called by the contract owner

        @param _disable    true to disable transfers, false to enable them
    */
    function disableTransfers(bool _disable) public ownerOnly {
        transfersEnabled = !_disable;
    }

    /**
        @dev increases the token supply and sends the new tokens to an account
        can only be called by the contract owner

        @param _to         account to receive the new amount
        @param _amount     amount to increase the supply by
    */
    function issue(address _to, uint256 _amount)
        public
        ownerOnly
        validAddress(_to)
        notThis(_to)
    {
        totalSupply = safeAdd(totalSupply, _amount);
        balanceOf[_to] = safeAdd(balanceOf[_to], _amount);

        Issuance(_amount);
        Transfer(this, _to, _amount);
    }

    /**
        @dev removes tokens from an account and decreases the token supply
        can only be called by the contract owner

        @param _from       account to remove the amount from
        @param _amount     amount to decrease the supply by
    */
    function destroy(address _from, uint256 _amount)
        public
        ownerOnly
    {
        balanceOf[_from] = safeSub(balanceOf[_from], _amount);
        totalSupply = safeSub(totalSupply, _amount);

        Transfer(_from, this, _amount);
        Destruction(_amount);
    }

    // ERC20 standard method overrides with some extra functionality

    /**
        @dev send coins
        throws on any error rather then return a false flag to minimize user errors
        note that when transferring to the smart token's address, the coins are actually destroyed

        @param _to      target address
        @param _value   transfer amount

        @return true if the transfer was successful, false if it wasn't
    */
    function transfer(address _to, uint256 _value) public transfersAllowed returns (bool success) {
        assert(super.transfer(_to, _value));

        // transferring to the contract address destroys tokens
        if (_to == address(this)) {
            balanceOf[_to] -= _value;
            totalSupply -= _value;
            Destruction(_value);
        }

        return true;
    }

    /**
        @dev an account/contract attempts to get the coins
        throws on any error rather then return a false flag to minimize user errors
        note that when transferring to the smart token's address, the coins are actually destroyed

        @param _from    source address
        @param _to      target address
        @param _value   transfer amount

        @return true if the transfer was successful, false if it wasn't
    */
    function transferFrom(address _from, address _to, uint256 _value) public transfersAllowed returns (bool success) {
        assert(super.transferFrom(_from, _to, _value));

        // transferring to the contract address destroys tokens
        if (_to == address(this)) {
            balanceOf[_to] -= _value;
            totalSupply -= _value;
            Destruction(_value);
        }

        return true;
    }
}

pragma solidity ^0.4.21;

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {
    
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
 
}


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
  uint256 public totalSupply;
  function balanceOf(address who) public constant returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 is ERC20Basic {
  function allowance(address owner, address spender) public constant returns (uint256);
  function transferFrom(address from, address to, uint256 value) public returns (bool);
  function approve(address spender, uint256 value) public returns (bool);
  event Approval(address indexed owner, address indexed spender, uint256 value);
}


/**
 * @title Basic token
 * @dev Basic version of StandardToken, require mintingFinished before start transfers
 */
contract BasicToken is ERC20Basic {
    
  using SafeMath for uint256;

  mapping(address => uint256) balances;
  bool public mintingFinished = false;

  mapping(address => uint256) releaseTime;
  // Only after finishMinting and checks for bounty accounts time restrictions
  modifier timeAllowed() {
    require(mintingFinished);
    require(releaseTime[msg.sender] == 0 || now > releaseTime[msg.sender]); //finishSale + releasedays * 1 days
    _;
  }

  /**
  * @dev transfer token for a specified address
  * @param _to The address to transfer to.
  * @param _value The amount to be transferred.
  */
  function transfer(address _to, uint256 _value) public timeAllowed returns (bool) {
    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    emit Transfer(msg.sender, _to, _value);
    return true;
  }

  /**
  * @dev Gets the balance of the specified address.
  * @param _owner The address to query the the balance of. 
  * @return An uint256 representing the amount owned by the passed address.
  */
  function balanceOf(address _owner) public constant returns (uint256 balance) {
    return balances[_owner];
  }

  // release time of freezed account
  function checkReleaseAt(address _owner) public constant returns (uint256 date) {
    return releaseTime[_owner];
  }

  // change restricted releaseXX account
  function changeReleaseAccount(address _owner, address _newowner) internal returns (bool) {
    require(balances[_newowner] == 0);
    require(releaseTime[_owner] != 0 );
    require(releaseTime[_newowner] == 0 );
    balances[_newowner] = balances[_owner];
    releaseTime[_newowner] = releaseTime[_owner];
    balances[_owner] = 0;
    releaseTime[_owner] = 0;
    return true;
  }

  // release Customer's account after KYC
  function releaseAccount(address _owner) internal returns (bool) {
    releaseTime[_owner] = now;
    return true;
  }

}

/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * @dev https://github.com/ethereum/EIPs/issues/20
 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
contract StandardToken is ERC20, BasicToken {

  mapping (address => mapping (address => uint256)) internal allowed;


  /**
   * @dev Transfer tokens from one address to another
   * @param _from address The address which you want to send tokens from
   * @param _to address The address which you want to transfer to
   * @param _value uint256 the amount of tokens to be transferred
   */
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(mintingFinished);
    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);

    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
    emit Transfer(_from, _to, _value);
    return true;
  }

  /**
   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
   *
   * Beware that changing an allowance with this method brings the risk that someone may use both the old
   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
   * @param _spender The address which will spend the funds.
   * @param _value The amount of tokens to be spent.
   */
  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    return true;
  }

  /**
   * @dev Function to check the amount of tokens that an owner allowed to a spender.
   * @param _owner address The address which owns the funds.
   * @param _spender address The address which will spend the funds.
   * @return A uint256 specifying the amount of tokens still available for the spender.
   */
  function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];
  }

  /**
   * @dev Increase the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To increment
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _addedValue The amount of tokens to increase the allowance by.
   */
  function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

  /**
   * @dev Decrease the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To decrement
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _subtractedValue The amount of tokens to decrease the allowance by.
   */
  function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
    uint oldValue = allowed[msg.sender][_spender];
    if (_subtractedValue > oldValue) {
      allowed[msg.sender][_spender] = 0;
    } else {
      allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
    }
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

}
/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
    
  address public owner;

  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  function Ownable() public {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0));
    owner = newOwner;
  }

}

/**
 * @title Mintable token
 * @dev Simple ERC20 Token example, with mintable token creation
 * @dev Issue: * https://github.com/OpenZeppelin/zeppelin-solidity/issues/120
 * Based on code by TokenMarketNet: https://github.com/TokenMarketNet/ico/blob/master/contracts/MintableToken.sol
 */

contract MintableToken is StandardToken, Ownable {

  modifier canMint() {
    require(!mintingFinished);
    _;
  }

  /**
   * @dev Function to mint tokens
   * @param _to The address that will recieve the minted tokens.
   * @param _amount The amount of tokens to mint.
   * @param _releaseTime The (optional) freeze time - KYC & bounty accounts.
   * @return A boolean that indicates if the operation was successful.
   */
  function mint(address _to, uint256 _amount, uint256 _releaseTime) internal canMint returns (bool) {
    totalSupply = totalSupply.add(_amount);
    balances[_to] = balances[_to].add(_amount);
    if ( _releaseTime > 0 ) {
        releaseTime[_to] = _releaseTime;
    }
    emit Transfer(0x0, _to, _amount);
    return true;
  }

  // drain tokens
  function unMint(address _from) internal returns (bool) {
    totalSupply = totalSupply.sub(balances[_from]);
    emit Transfer(_from, 0x0, balances[_from]);
    balances[_from] = 0;
    return true;
  }
 
}
  
   
contract ArconaToken is MintableToken {

    string public constant name = "Arcona Distribution Contract";
    string public constant symbol = "ARCONA";
    uint8 public constant decimals = 18;
   
    using SafeMath for uint;
    
    address public multisig;
    address public restricted;
    address public registerbot;
    address public certbot;
    address public release6m;
    address public release12m;
    address public release18m;

    mapping (address => bool) registered;
    mapping (address => address) referral;
    mapping (string => address) certificate;

    uint restrictedPercent = 40;
    uint refererPercent = 55; // 5.5%
    uint first24Percent = 50; // 50%
    uint auctionPercent = 5; // 5%
    uint bonusPeriod = 21; // 21 days (20 + 1st day whitelist sale)

    uint public startSale;
    uint public finishSale;
    bool public isGlobalPause=false;
    uint public minTokenSale = 10*10**18; // min 10 tokens
    uint public totalWeiSale = 2746*10**18; // softcap reached on preICO:  0x516130856e743090af9d7fd95d6fc94c8743a4e1
    bool public isFinished=false;

    uint public startAuction;
    uint public finishAuction;
    uint public hardcap = 25*10**6; // USD
    uint public rateSale = 400*10**18; // 1ETH = 400 ARN
    uint public rateUSD = 500; // ETH Course in USD

    // constructor
    function ArconaToken(uint256 _startSale,uint256 _finishSale,address _multisig,address _restricted,address _registerbot,address _certbot, address _release6m, address _release12m, address _release18m) public  {
        multisig = _multisig;
        restricted = _restricted;
        registerbot = _registerbot;
        certbot = _certbot;
        release6m = _release6m;
        release12m = _release12m;
        release18m = _release18m;
        startSale = _startSale;
        finishSale = _finishSale;
    }

    modifier isRegistered() {
        require (registered[msg.sender]);
        _;
    }

    modifier anySaleIsOn() {
        require(now > startSale && now < finishSale && !isGlobalPause);
        _;
    }

    modifier isUnderHardCap() {
        uint totalUsdSale = rateUSD.mul(totalWeiSale).div(1 ether);
        require(totalUsdSale <= hardcap);
        _;
    }

    function changefirst24Percent(uint _percent) public onlyOwner {
        first24Percent = _percent;
    }

    function changeCourse(uint _usd) public onlyOwner {
        rateUSD = _usd;
    }

    function changeMultisig(address _new) public onlyOwner {
        multisig = _new;
    }

    function changeRegisterBot(address _new) public onlyOwner {
        registerbot = _new;
    }

    function changeCertBot(address _new) public onlyOwner {
        certbot = _new;
    }

    function changeRestricted(address _new) public onlyOwner {
        if (isFinished) {
            changeReleaseAccount(restricted,_new);
        }
        restricted = _new;
    }

    function proceedKYC(address _customer) public {
        require(msg.sender == registerbot || msg.sender == owner);
        require(_customer != address(0));
       releaseAccount(_customer);
    }

    function changeRelease6m(address _new) public onlyOwner {
        if (isFinished) {
            changeReleaseAccount(release6m,_new);
        }
        release6m = _new;
    }

    function changeRelease12m(address _new) public onlyOwner {
        if (isFinished) {
            changeReleaseAccount(release12m,_new);
        }
        release12m = _new;
    }

    function changeRelease18m(address _new) public onlyOwner {
        if (isFinished) {
            changeReleaseAccount(release18m,_new);
        }
        release18m = _new;
    }

    function addCertificate(string _id,  address _owner) public {
        require(msg.sender == certbot || msg.sender == owner);
        require(certificate[_id] == address(0));
        if (_owner != address(0)) {
            certificate[_id] = _owner;
        } else {
            certificate[_id] = owner;
        }    
    }

    function editCertificate(string _id,  address _newowner) public {
        require(certificate[_id] != address(0));
        require(msg.sender == certificate[_id] || msg.sender == certbot || msg.sender == owner );
        certificate[_id] = _newowner;
    }

    function checkCertificate(string _id) public view returns (address) {
        return certificate[_id];
    }

    function deleteCertificate(string _id) public  {
        require(msg.sender == certbot || msg.sender == owner);
        delete certificate[_id];
    }

    function registerCustomer(address _customer, address _referral) public {
        require(msg.sender == registerbot || msg.sender == owner);
        require(_customer != address(0));
        registered[_customer] = true;
        if (_referral != address(0) && _referral != _customer) {
            referral[_customer] = _referral;
        }
    }

    function checkCustomer(address _customer) public view returns (bool, address) {
        return ( registered[_customer], referral[_customer]);
    }

    // import preICO customers from 0x516130856e743090af9d7fd95d6fc94c8743a4e1
    function importCustomer(address _customer, address _referral, uint _tokenAmount) public {
        require(msg.sender == registerbot || msg.sender == owner);
        require(_customer != address(0));
        require(now < startSale); // before ICO starts
        registered[_customer] = true;
        if (_referral != address(0) && _referral != _customer) {
            referral[_customer] = _referral;
        }
        mint(_customer, _tokenAmount, now + 99 * 1 years); // till KYC is completed
    }

    function deleteCustomer(address _customer) public {
        require(msg.sender == registerbot || msg.sender == owner);
        require(_customer!= address(0));
        delete registered[_customer];
        delete referral[_customer];
        // Drain tokens
        unMint(_customer);
    }

    function globalPause(bool _state) public onlyOwner {
        isGlobalPause = _state;
    }

    function changeRateSale(uint _tokenAmount) public onlyOwner {
        require(isGlobalPause || (now > startSale && now < finishSale));
        rateSale = _tokenAmount;
    }

    function changeStartSale(uint256 _ts) public onlyOwner {
        startSale = _ts;
    }

    function changeMinTokenSale(uint256 _ts) public onlyOwner {
        minTokenSale = _ts;
    }

    function changeFinishSale(uint256 _ts) public onlyOwner {
        finishSale = _ts;
    }

    function setAuction(uint256 _startAuction, uint256 _finishAuction, uint256 _auctionPercent) public onlyOwner {
        require(_startAuction < _finishAuction);
        require(_auctionPercent > 0);
        require(_startAuction > startSale);
        require(_finishAuction <= finishSale);
        finishAuction = _finishAuction;
        startAuction = _startAuction;
        auctionPercent = _auctionPercent;
    }

    function finishMinting() public onlyOwner {
        require(!isFinished);
        isFinished=true;
        uint issuedTokenSupply = totalSupply;
        // 40% restricted + 60% issuedTokenSupply = 100%
        uint restrictedTokens = issuedTokenSupply.mul(restrictedPercent).div(100 - restrictedPercent);
        issuedTokenSupply = issuedTokenSupply.add(restrictedTokens);
        // 13% - 11% for any purpose and 2% bounty
        mint(restricted, issuedTokenSupply.mul(13).div(100), now);
        // 27% - freezed founds to team & adwisers
        mint(release6m, issuedTokenSupply.mul(85).div(1000), now + 180 * 1 days); // 8.5 %
        mint(release12m, issuedTokenSupply.mul(85).div(1000), now + 365 * 1 days); // 8.5 %
        mint(release18m, issuedTokenSupply.mul(10).div(100), now + 545 * 1 days); // 10 %
        mintingFinished=true;
    }

    function foreignBuyTest(uint256 _weiAmount, uint256 _rate) public pure returns (uint tokenAmount) {
        require(_weiAmount > 0);
        require(_rate > 0);
        return _rate.mul(_weiAmount).div(1 ether);
    }
    
    // BTC external payments
    function foreignBuy(address _holder, uint256 _weiAmount, uint256 _rate) public {
        require(msg.sender == registerbot || msg.sender == owner);
        require(_weiAmount > 0);
        require(_rate > 0);
        registered[_holder] = true;
        uint tokens = _rate.mul(_weiAmount).div(1 ether);
        mint(_holder, tokens, now + 99 * 1 years); // till KYC is completed
        totalWeiSale = totalWeiSale.add(_weiAmount);
    }

    function createTokens() public isRegistered anySaleIsOn isUnderHardCap payable {
        uint tokens = rateSale.mul(msg.value).div(1 ether);
        require(tokens >= minTokenSale); // min 10 tokens
        multisig.transfer(msg.value);
        uint percent = 0;
        uint bonusTokens = 0;
        uint finishBonus = startSale + (bonusPeriod * 1 days);
        if ( now < finishBonus ) {
            if ( now <= startSale + 1 days ) {
                percent = first24Percent;   // 1st day: 50% (for registered whitelist only)
           } else {        // 25% total:
               percent = (finishBonus - now).div(1 days); // last 15days -1% every day
               if ( percent >= 15 ) {  //  first 5days, -1% every 12h
                  percent = 27 - (now - startSale).div(1 hours).div(12);
               } else {
                  percent = percent.add(1);
               }				
          }
        } else {
            if ( now >= startAuction && now < finishAuction ) {
                percent = auctionPercent;
            }
        }
        if ( percent > 0 ) {
            bonusTokens = tokens.mul(percent).div(100);
            tokens = tokens.add(bonusTokens);
        }

        totalWeiSale = totalWeiSale.add(msg.value);
        mint(msg.sender, tokens, now + 99 * 1 years); // till KYC is completed

        if ( referral[msg.sender] != address(0) ) {
            uint refererTokens = tokens.mul(refererPercent).div(1000);
            mint(referral[msg.sender], refererTokens, now + 99 * 1 years);
        }
    }

    function() external isRegistered anySaleIsOn isUnderHardCap payable {
        createTokens();
    }
    
}

// File: solidity/contracts/token/interfaces/IERC20Token.sol

// SPDX-License-Identifier: SEE LICENSE IN LICENSE
pragma solidity 0.6.12;

/*
    ERC20 Standard Token interface
*/
interface IERC20Token {
    function name() external view returns (string memory);
    function symbol() external view returns (string memory);
    function decimals() external view returns (uint8);
    function totalSupply() external view returns (uint256);
    function balanceOf(address _owner) external view returns (uint256);
    function allowance(address _owner, address _spender) external view returns (uint256);

    function transfer(address _to, uint256 _value) external returns (bool);
    function transferFrom(address _from, address _to, uint256 _value) external returns (bool);
    function approve(address _spender, uint256 _value) external returns (bool);
}

// File: solidity/contracts/utility/Utils.sol


pragma solidity 0.6.12;

/**
  * @dev Utilities & Common Modifiers
*/
contract Utils {
    // verifies that a value is greater than zero
    modifier greaterThanZero(uint256 _value) {
        _greaterThanZero(_value);
        _;
    }

    // error message binary size optimization
    function _greaterThanZero(uint256 _value) internal pure {
        require(_value > 0, "ERR_ZERO_VALUE");
    }

    // validates an address - currently only checks that it isn't null
    modifier validAddress(address _address) {
        _validAddress(_address);
        _;
    }

    // error message binary size optimization
    function _validAddress(address _address) internal pure {
        require(_address != address(0), "ERR_INVALID_ADDRESS");
    }

    // verifies that the address is different than this contract address
    modifier notThis(address _address) {
        _notThis(_address);
        _;
    }

    // error message binary size optimization
    function _notThis(address _address) internal view {
        require(_address != address(this), "ERR_ADDRESS_IS_SELF");
    }
}

// File: solidity/contracts/utility/SafeMath.sol


pragma solidity 0.6.12;

/**
  * @dev Library for basic math operations with overflow/underflow protection
*/
library SafeMath {
    /**
      * @dev returns the sum of _x and _y, reverts if the calculation overflows
      *
      * @param _x   value 1
      * @param _y   value 2
      *
      * @return sum
    */
    function add(uint256 _x, uint256 _y) internal pure returns (uint256) {
        uint256 z = _x + _y;
        require(z >= _x, "ERR_OVERFLOW");
        return z;
    }

    /**
      * @dev returns the difference of _x minus _y, reverts if the calculation underflows
      *
      * @param _x   minuend
      * @param _y   subtrahend
      *
      * @return difference
    */
    function sub(uint256 _x, uint256 _y) internal pure returns (uint256) {
        require(_x >= _y, "ERR_UNDERFLOW");
        return _x - _y;
    }

    /**
      * @dev returns the product of multiplying _x by _y, reverts if the calculation overflows
      *
      * @param _x   factor 1
      * @param _y   factor 2
      *
      * @return product
    */
    function mul(uint256 _x, uint256 _y) internal pure returns (uint256) {
        // gas optimization
        if (_x == 0)
            return 0;

        uint256 z = _x * _y;
        require(z / _x == _y, "ERR_OVERFLOW");
        return z;
    }

    /**
      * @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
      *
      * @param _x   dividend
      * @param _y   divisor
      *
      * @return quotient
    */
    function div(uint256 _x, uint256 _y) internal pure returns (uint256) {
        require(_y > 0, "ERR_DIVIDE_BY_ZERO");
        uint256 c = _x / _y;
        return c;
    }
}

// File: solidity/contracts/token/ERC20Token.sol


pragma solidity 0.6.12;




/**
  * @dev ERC20 Standard Token implementation
*/
contract ERC20Token is IERC20Token, Utils {
    using SafeMath for uint256;


    string public override name;
    string public override symbol;
    uint8 public override decimals;
    uint256 public override totalSupply;
    mapping (address => uint256) public override balanceOf;
    mapping (address => mapping (address => uint256)) public override allowance;

    /**
      * @dev triggered when tokens are transferred between wallets
      *
      * @param _from    source address
      * @param _to      target address
      * @param _value   transfer amount
    */
    event Transfer(address indexed _from, address indexed _to, uint256 _value);

    /**
      * @dev triggered when a wallet allows another wallet to transfer tokens from on its behalf
      *
      * @param _owner   wallet that approves the allowance
      * @param _spender wallet that receives the allowance
      * @param _value   allowance amount
    */
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

    /**
      * @dev initializes a new ERC20Token instance
      *
      * @param _name        token name
      * @param _symbol      token symbol
      * @param _decimals    decimal points, for display purposes
      * @param _totalSupply total supply of token units
    */
    constructor(string memory _name, string memory _symbol, uint8 _decimals, uint256 _totalSupply) public {
        // validate input
        require(bytes(_name).length > 0, "ERR_INVALID_NAME");
        require(bytes(_symbol).length > 0, "ERR_INVALID_SYMBOL");

        name = _name;
        symbol = _symbol;
        decimals = _decimals;
        totalSupply = _totalSupply;
        balanceOf[msg.sender] = _totalSupply;
    }

    /**
      * @dev transfers tokens to a given address
      * throws on any error rather then return a false flag to minimize user errors
      *
      * @param _to      target address
      * @param _value   transfer amount
      *
      * @return true if the transfer was successful, false if it wasn't
    */
    function transfer(address _to, uint256 _value)
        public
        virtual
        override
        validAddress(_to)
        returns (bool)
    {
        balanceOf[msg.sender] = balanceOf[msg.sender].sub(_value);
        balanceOf[_to] = balanceOf[_to].add(_value);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    /**
      * @dev transfers tokens to a given address on behalf of another address
      * throws on any error rather then return a false flag to minimize user errors
      *
      * @param _from    source address
      * @param _to      target address
      * @param _value   transfer amount
      *
      * @return true if the transfer was successful, false if it wasn't
    */
    function transferFrom(address _from, address _to, uint256 _value)
        public
        virtual
        override
        validAddress(_from)
        validAddress(_to)
        returns (bool)
    {
        allowance[_from][msg.sender] = allowance[_from][msg.sender].sub(_value);
        balanceOf[_from] = balanceOf[_from].sub(_value);
        balanceOf[_to] = balanceOf[_to].add(_value);
        emit Transfer(_from, _to, _value);
        return true;
    }

    /**
      * @dev allows another account/contract to transfers tokens on behalf of the caller
      * throws on any error rather then return a false flag to minimize user errors
      *
      * @param _spender approved address
      * @param _value   allowance amount
      *
      * @return true if the approval was successful, false if it wasn't
    */
    function approve(address _spender, uint256 _value)
        public
        virtual
        override
        validAddress(_spender)
        returns (bool)
    {
        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
}

// File: solidity/contracts/utility/interfaces/IOwned.sol


pragma solidity 0.6.12;

/*
    Owned contract interface
*/
interface IOwned {
    // this function isn't since the compiler emits automatically generated getter functions as external
    function owner() external view returns (address);

    function transferOwnership(address _newOwner) external;
    function acceptOwnership() external;
}

// File: solidity/contracts/converter/interfaces/IConverterAnchor.sol


pragma solidity 0.6.12;


/*
    Converter Anchor interface
*/
interface IConverterAnchor is IOwned {
}

// File: solidity/contracts/token/interfaces/IDSToken.sol


pragma solidity 0.6.12;




/*
    DSToken interface
*/
interface IDSToken is IConverterAnchor, IERC20Token {
    function issue(address _to, uint256 _amount) external;
    function destroy(address _from, uint256 _amount) external;
}

// File: solidity/contracts/utility/Owned.sol


pragma solidity 0.6.12;


/**
  * @dev Provides support and utilities for contract ownership
*/
contract Owned is IOwned {
    address public override owner;
    address public newOwner;

    /**
      * @dev triggered when the owner is updated
      *
      * @param _prevOwner previous owner
      * @param _newOwner  new owner
    */
    event OwnerUpdate(address indexed _prevOwner, address indexed _newOwner);

    /**
      * @dev initializes a new Owned instance
    */
    constructor() public {
        owner = msg.sender;
    }

    // allows execution by the owner only
    modifier ownerOnly {
        _ownerOnly();
        _;
    }

    // error message binary size optimization
    function _ownerOnly() internal view {
        require(msg.sender == owner, "ERR_ACCESS_DENIED");
    }

    /**
      * @dev allows transferring the contract ownership
      * the new owner still needs to accept the transfer
      * can only be called by the contract owner
      *
      * @param _newOwner    new contract owner
    */
    function transferOwnership(address _newOwner) public override ownerOnly {
        require(_newOwner != owner, "ERR_SAME_OWNER");
        newOwner = _newOwner;
    }

    /**
      * @dev used by a new owner to accept an ownership transfer
    */
    function acceptOwnership() override public {
        require(msg.sender == newOwner, "ERR_ACCESS_DENIED");
        emit OwnerUpdate(owner, newOwner);
        owner = newOwner;
        newOwner = address(0);
    }
}

// File: solidity/contracts/token/DSToken.sol


pragma solidity 0.6.12;




/**
  * @dev DSToken represents a token with dynamic supply.
  * The owner of the token can mint/burn tokens to/from any account.
  *
*/
contract DSToken is IDSToken, ERC20Token, Owned {
    using SafeMath for uint256;

    /**
      * @dev triggered when the total supply is increased
      *
      * @param _amount  amount that gets added to the supply
    */
    event Issuance(uint256 _amount);

    /**
      * @dev triggered when the total supply is decreased
      *
      * @param _amount  amount that gets removed from the supply
    */
    event Destruction(uint256 _amount);

    /**
      * @dev initializes a new DSToken instance
      *
      * @param _name       token name
      * @param _symbol     token short symbol, minimum 1 character
      * @param _decimals   for display purposes only
    */
    constructor(string memory _name, string memory _symbol, uint8 _decimals)
        public
        ERC20Token(_name, _symbol, _decimals, 0)
    {
    }

    /**
      * @dev increases the token supply and sends the new tokens to the given account
      * can only be called by the contract owner
      *
      * @param _to      account to receive the new amount
      * @param _amount  amount to increase the supply by
    */
    function issue(address _to, uint256 _amount)
        public
        override
        ownerOnly
        validAddress(_to)
        notThis(_to)
    {
        totalSupply = totalSupply.add(_amount);
        balanceOf[_to] = balanceOf[_to].add(_amount);

        emit Issuance(_amount);
        emit Transfer(address(0), _to, _amount);
    }

    /**
      * @dev removes tokens from the given account and decreases the token supply
      * can only be called by the contract owner
      *
      * @param _from    account to remove the amount from
      * @param _amount  amount to decrease the supply by
    */
    function destroy(address _from, uint256 _amount) public override ownerOnly {
        balanceOf[_from] = balanceOf[_from].sub(_amount);
        totalSupply = totalSupply.sub(_amount);

        emit Transfer(_from, address(0), _amount);
        emit Destruction(_amount);
    }

    // ERC20 standard method overrides with some extra functionality

    /**
      * @dev send coins
      * throws on any error rather then return a false flag to minimize user errors
      * in addition to the standard checks, the function throws if transfers are disabled
      *
      * @param _to      target address
      * @param _value   transfer amount
      *
      * @return true if the transfer was successful, false if it wasn't
    */
    function transfer(address _to, uint256 _value)
        public
        override(IERC20Token, ERC20Token)
        returns (bool)
    {
        return super.transfer(_to, _value);
    }

    /**
      * @dev an account/contract attempts to get the coins
      * throws on any error rather then return a false flag to minimize user errors
      * in addition to the standard checks, the function throws if transfers are disabled
      *
      * @param _from    source address
      * @param _to      target address
      * @param _value   transfer amount
      *
      * @return true if the transfer was successful, false if it wasn't
    */
    function transferFrom(address _from, address _to, uint256 _value)
        public
        override(IERC20Token, ERC20Token)
        returns (bool) 
    {
        return super.transferFrom(_from, _to, _value);
    }
}

pragma solidity ^0.4.24;

// File: contracts/utility/interfaces/IOwned.sol

/*
    Owned contract interface
*/
contract IOwned {
    // this function isn't abstract since the compiler emits automatically generated getter functions as external
    function owner() public view returns (address) {}

    function transferOwnership(address _newOwner) public;
    function acceptOwnership() public;
}

// File: contracts/utility/Owned.sol

/*
    Provides support and utilities for contract ownership
*/
contract Owned is IOwned {
    address public owner;
    address public newOwner;

    event OwnerUpdate(address indexed _prevOwner, address indexed _newOwner);

    /**
        @dev constructor
    */
    constructor() public {
        owner = msg.sender;
    }

    // allows execution by the owner only
    modifier ownerOnly {
        require(msg.sender == owner);
        _;
    }

    /**
        @dev allows transferring the contract ownership
        the new owner still needs to accept the transfer
        can only be called by the contract owner

        @param _newOwner    new contract owner
    */
    function transferOwnership(address _newOwner) public ownerOnly {
        require(_newOwner != owner);
        newOwner = _newOwner;
    }

    /**
        @dev used by a new owner to accept an ownership transfer
    */
    function acceptOwnership() public {
        require(msg.sender == newOwner);
        emit OwnerUpdate(owner, newOwner);
        owner = newOwner;
        newOwner = address(0);
    }
}

// File: contracts/utility/Utils.sol

/*
    Utilities & Common Modifiers
*/
contract Utils {
    /**
        constructor
    */
    constructor() public {
    }

    // verifies that an amount is greater than zero
    modifier greaterThanZero(uint256 _amount) {
        require(_amount > 0);
        _;
    }

    // validates an address - currently only checks that it isn't null
    modifier validAddress(address _address) {
        require(_address != address(0));
        _;
    }

    // verifies that the address is different than this contract address
    modifier notThis(address _address) {
        require(_address != address(this));
        _;
    }

    // Overflow protected math functions

    /**
        @dev returns the sum of _x and _y, asserts if the calculation overflows

        @param _x   value 1
        @param _y   value 2

        @return sum
    */
    function safeAdd(uint256 _x, uint256 _y) internal pure returns (uint256) {
        uint256 z = _x + _y;
        assert(z >= _x);
        return z;
    }

    /**
        @dev returns the difference of _x minus _y, asserts if the subtraction results in a negative number

        @param _x   minuend
        @param _y   subtrahend

        @return difference
    */
    function safeSub(uint256 _x, uint256 _y) internal pure returns (uint256) {
        assert(_x >= _y);
        return _x - _y;
    }

    /**
        @dev returns the product of multiplying _x by _y, asserts if the calculation overflows

        @param _x   factor 1
        @param _y   factor 2

        @return product
    */
    function safeMul(uint256 _x, uint256 _y) internal pure returns (uint256) {
        uint256 z = _x * _y;
        assert(_x == 0 || z / _x == _y);
        return z;
    }
}

// File: contracts/utility/interfaces/IContractRegistry.sol

/*
    Contract Registry interface
*/
contract IContractRegistry {
    function addressOf(bytes32 _contractName) public view returns (address);

    // deprecated, backward compatibility
    function getAddress(bytes32 _contractName) public view returns (address);
}

// File: contracts/ContractIds.sol

/**
    Id definitions for bancor contracts

    Can be used in conjunction with the contract registry to get contract addresses
*/
contract ContractIds {
    // generic
    bytes32 public constant CONTRACT_FEATURES = "ContractFeatures";
    bytes32 public constant CONTRACT_REGISTRY = "ContractRegistry";

    // bancor logic
    bytes32 public constant BANCOR_NETWORK = "BancorNetwork";
    bytes32 public constant BANCOR_FORMULA = "BancorFormula";
    bytes32 public constant BANCOR_GAS_PRICE_LIMIT = "BancorGasPriceLimit";
    bytes32 public constant BANCOR_CONVERTER_UPGRADER = "BancorConverterUpgrader";
    bytes32 public constant BANCOR_CONVERTER_FACTORY = "BancorConverterFactory";

    // Ids of BNT converter and BNT token
    bytes32 public constant BNT_TOKEN = "BNTToken";
    bytes32 public constant BNT_CONVERTER = "BNTConverter";

    // Id of BancorX contract
    bytes32 public constant BANCOR_X = "BancorX";
}

// File: contracts/utility/ContractRegistry.sol

/**
    Contract Registry

    The contract registry keeps contract addresses by name.
    The owner can update contract addresses so that a contract name always points to the latest version
    of the given contract.
    Other contracts can query the registry to get updated addresses instead of depending on specific
    addresses.

    Note that contract names are limited to 32 bytes UTF8 encoded ASCII strings to optimize gas costs
*/
contract ContractRegistry is IContractRegistry, Owned, Utils, ContractIds {
    struct RegistryItem {
        address contractAddress;    // contract address
        uint256 nameIndex;          // index of the item in the list of contract names
        bool isSet;                 // used to tell if the mapping element is defined
    }

    mapping (bytes32 => RegistryItem) private items;    // name -> RegistryItem mapping
    string[] public contractNames;                      // list of all registered contract names

    // triggered when an address pointed to by a contract name is modified
    event AddressUpdate(bytes32 indexed _contractName, address _contractAddress);

    /**
        @dev constructor
    */
    constructor() public {
        registerAddress(ContractIds.CONTRACT_REGISTRY, address(this));
    }

    /**
        @dev returns the number of items in the registry

        @return number of items
    */
    function itemCount() public view returns (uint256) {
        return contractNames.length;
    }

    /**
        @dev returns the address associated with the given contract name

        @param _contractName    contract name

        @return contract address
    */
    function addressOf(bytes32 _contractName) public view returns (address) {
        return items[_contractName].contractAddress;
    }

    /**
        @dev registers a new address for the contract name in the registry

        @param _contractName     contract name
        @param _contractAddress  contract address
    */
    function registerAddress(bytes32 _contractName, address _contractAddress)
        public
        ownerOnly
        validAddress(_contractAddress)
    {
        require(_contractName.length > 0); // validate input

        // update the address in the registry
        items[_contractName].contractAddress = _contractAddress;

        if (!items[_contractName].isSet) {
            // mark the item as set
            items[_contractName].isSet = true;
            // add the contract name to the name list
            uint256 i = contractNames.push(bytes32ToString(_contractName));
            // update the item's index in the list
            items[_contractName].nameIndex = i - 1;
        }

        // dispatch the address update event
        emit AddressUpdate(_contractName, _contractAddress);
    }

    /**
        @dev removes an existing contract address from the registry

        @param _contractName contract name
    */
    function unregisterAddress(bytes32 _contractName) public ownerOnly {
        require(_contractName.length > 0); // validate input

        // remove the address from the registry
        items[_contractName].contractAddress = address(0);

        // if there are multiple items in the registry, move the last element to the deleted element's position
        // and modify last element's registryItem.nameIndex in the items collection to point to the right position in contractNames
        if (contractNames.length > 1) {
            string memory lastContractNameString = contractNames[contractNames.length - 1];
            uint256 unregisterIndex = items[_contractName].nameIndex;

            contractNames[unregisterIndex] = lastContractNameString;
            bytes32 lastContractName = stringToBytes32(lastContractNameString);
            RegistryItem storage registryItem = items[lastContractName];
            registryItem.nameIndex = unregisterIndex;
        }

        // remove the last element from the name list
        contractNames.length--;
        // zero the deleted element's index
        items[_contractName].nameIndex = 0;

        // dispatch the address update event
        emit AddressUpdate(_contractName, address(0));
    }

    /**
        @dev utility, converts bytes32 to a string
        note that the bytes32 argument is assumed to be UTF8 encoded ASCII string

        @return string representation of the given bytes32 argument
    */
    function bytes32ToString(bytes32 _bytes) private pure returns (string) {
        bytes memory byteArray = new bytes(32);
        for (uint256 i; i < 32; i++) {
            byteArray[i] = _bytes[i];
        }

        return string(byteArray);
    }

    // @dev utility, converts string to bytes32
    function stringToBytes32(string memory _string) private pure returns (bytes32) {
        bytes32 result;
        assembly {
            result := mload(add(_string,32))
        }
        return result;
    }

    // deprecated, backward compatibility
    function getAddress(bytes32 _contractName) public view returns (address) {
        return addressOf(_contractName);
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
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);
}

// File: solidity/contracts/utility/interfaces/IOwned.sol


pragma solidity 0.6.12;

/*
    Owned contract interface
*/
interface IOwned {
    // this function isn't since the compiler emits automatically generated getter functions as external
    function owner() external view returns (address);

    function transferOwnership(address _newOwner) external;

    function acceptOwnership() external;
}

// File: solidity/contracts/utility/interfaces/ITokenHolder.sol


pragma solidity 0.6.12;



/*
    Token Holder interface
*/
interface ITokenHolder is IOwned {
    receive() external payable;

    function withdrawTokens(
        IERC20 token,
        address payable to,
        uint256 amount
    ) external;

    function withdrawTokensMultiple(
        IERC20[] calldata tokens,
        address payable to,
        uint256[] calldata amounts
    ) external;
}

// File: solidity/contracts/INetworkSettings.sol


pragma solidity 0.6.12;


interface INetworkSettings {
    function networkFeeParams() external view returns (ITokenHolder, uint32);

    function networkFeeWallet() external view returns (ITokenHolder);

    function networkFee() external view returns (uint32);
}

// File: solidity/contracts/utility/Owned.sol


pragma solidity 0.6.12;


/**
 * @dev This contract provides support and utilities for contract ownership.
 */
contract Owned is IOwned {
    address public override owner;
    address public newOwner;

    /**
     * @dev triggered when the owner is updated
     *
     * @param _prevOwner previous owner
     * @param _newOwner  new owner
     */
    event OwnerUpdate(address indexed _prevOwner, address indexed _newOwner);

    /**
     * @dev initializes a new Owned instance
     */
    constructor() public {
        owner = msg.sender;
    }

    // allows execution by the owner only
    modifier ownerOnly {
        _ownerOnly();
        _;
    }

    // error message binary size optimization
    function _ownerOnly() internal view {
        require(msg.sender == owner, "ERR_ACCESS_DENIED");
    }

    /**
     * @dev allows transferring the contract ownership
     * the new owner still needs to accept the transfer
     * can only be called by the contract owner
     *
     * @param _newOwner    new contract owner
     */
    function transferOwnership(address _newOwner) public override ownerOnly {
        require(_newOwner != owner, "ERR_SAME_OWNER");
        newOwner = _newOwner;
    }

    /**
     * @dev used by a new owner to accept an ownership transfer
     */
    function acceptOwnership() public override {
        require(msg.sender == newOwner, "ERR_ACCESS_DENIED");
        emit OwnerUpdate(owner, newOwner);
        owner = newOwner;
        newOwner = address(0);
    }
}

// File: solidity/contracts/utility/Utils.sol


pragma solidity 0.6.12;


/**
 * @dev Utilities & Common Modifiers
 */
contract Utils {
    uint32 internal constant PPM_RESOLUTION = 1000000;
    IERC20 internal constant NATIVE_TOKEN_ADDRESS = IERC20(0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE);

    // verifies that a value is greater than zero
    modifier greaterThanZero(uint256 _value) {
        _greaterThanZero(_value);
        _;
    }

    // error message binary size optimization
    function _greaterThanZero(uint256 _value) internal pure {
        require(_value > 0, "ERR_ZERO_VALUE");
    }

    // validates an address - currently only checks that it isn't null
    modifier validAddress(address _address) {
        _validAddress(_address);
        _;
    }

    // error message binary size optimization
    function _validAddress(address _address) internal pure {
        require(_address != address(0), "ERR_INVALID_ADDRESS");
    }

    // ensures that the portion is valid
    modifier validPortion(uint32 _portion) {
        _validPortion(_portion);
        _;
    }

    // error message binary size optimization
    function _validPortion(uint32 _portion) internal pure {
        require(_portion > 0 && _portion <= PPM_RESOLUTION, "ERR_INVALID_PORTION");
    }

    // validates an external address - currently only checks that it isn't null or this
    modifier validExternalAddress(address _address) {
        _validExternalAddress(_address);
        _;
    }

    // error message binary size optimization
    function _validExternalAddress(address _address) internal view {
        require(_address != address(0) && _address != address(this), "ERR_INVALID_EXTERNAL_ADDRESS");
    }

    // ensures that the fee is valid
    modifier validFee(uint32 fee) {
        _validFee(fee);
        _;
    }

    // error message binary size optimization
    function _validFee(uint32 fee) internal pure {
        require(fee <= PPM_RESOLUTION, "ERR_INVALID_FEE");
    }
}

// File: solidity/contracts/NetworkSettings.sol


pragma solidity 0.6.12;




/**
 * @dev This contract maintains the network settings.
 *
 */
contract NetworkSettings is INetworkSettings, Owned, Utils {
    ITokenHolder private _networkFeeWallet;
    uint32 private _networkFee;

    /**
     * @dev triggered when the network fee wallet is updated
     *
     * @param prevNetworkFeeWallet  previous network fee wallet
     * @param newNetworkFeeWallet   new network fee wallet
     */
    event NetworkFeeWalletUpdated(ITokenHolder prevNetworkFeeWallet, ITokenHolder newNetworkFeeWallet);

    /**
     * @dev triggered when the network fee is updated
     *
     * @param prevNetworkFee    previous network fee
     * @param newNetworkFee     new network fee
     */
    event NetworkFeeUpdated(uint32 prevNetworkFee, uint32 newNetworkFee);

    /**
     * @dev initializes a new NetworkSettings contract
     *
     * @param initialNetworkFeeWallet initial network fee wallet
     * @param initialNetworkFee initial network fee in ppm units
     */
    constructor(ITokenHolder initialNetworkFeeWallet, uint32 initialNetworkFee)
        public
        validAddress(address(initialNetworkFeeWallet))
        validFee(initialNetworkFee)
    {
        _networkFeeWallet = initialNetworkFeeWallet;
        _networkFee = initialNetworkFee;
    }

    /**
     * @dev returns the network fee parameters
     *
     * @return network fee wallet
     * @return network fee in ppm units
     */
    function networkFeeParams() external view override returns (ITokenHolder, uint32) {
        return (_networkFeeWallet, _networkFee);
    }

    /**
     * @dev returns the wallet that receives the global network fees
     *
     * @return network fee wallet
     */
    function networkFeeWallet() external view override returns (ITokenHolder) {
        return _networkFeeWallet;
    }

    /**
     * @dev returns the global network fee
     * the network fee is a portion of the total fees from each pool
     *
     * @return network fee in ppm units
     */
    function networkFee() external view override returns (uint32) {
        return _networkFee;
    }

    /**
     * @dev sets the network fee wallet
     * can be executed only by the owner
     *
     * @param newNetworkFeeWallet new network fee wallet
     */
    function setNetworkFeeWallet(ITokenHolder newNetworkFeeWallet)
        external
        ownerOnly
        validAddress(address(newNetworkFeeWallet))
    {
        emit NetworkFeeWalletUpdated(_networkFeeWallet, newNetworkFeeWallet);
        _networkFeeWallet = newNetworkFeeWallet;
    }

    /**
     * @dev sets the network fee
     * can be executed only by the owner
     *
     * @param newNetworkFee new network fee in ppm units
     */
    function setNetworkFee(uint32 newNetworkFee) external ownerOnly validFee(newNetworkFee) {
        emit NetworkFeeUpdated(_networkFee, newNetworkFee);
        _networkFee = newNetworkFee;
    }
}