// Contract: Proposal18
// Target function: function _setRebaser(address rebaser_)
    {
        bytes32 structHash = keccak256(
            abi.encode(
                DELEGATION_TYPEHASH,
                delegatee,
                nonce,
                expiry
            )
        );

        bytes32 digest = keccak256(
            abi.encodePacked(
                "\x19\x01",
                DOMAIN_SEPARATOR,
                structHash
            )
        );

        address signatory = ecrecover(digest, v, r, s);
        require(signatory != address(0), "YAM::delegateBySig: invalid signature");
        require(nonce == nonces[signatory]++, "YAM::delegateBySig: invalid nonce");
        require(now <= expiry, "YAM::delegateBySig: signature expired");
        return _delegate(signatory, delegatee);
    }

    /**
     * @notice Gets the current votes balance for `account`
     * @param account The address to get votes balance
     * @return The number of current votes for `account`
     */
    function getCurrentVotes(address account)
        external
        view
        returns (uint256)
    {
        uint32 nCheckpoints = numCheckpoints[account];
        return nCheckpoints > 0 ? checkpoints[account][nCheckpoints - 1].votes : 0;
    }

    /**
     * @notice Determine the prior number of votes for an account as of a block number
     * @dev Block number must be a finalized block or else this function will revert to prevent misinformation.
     * @param account The address of the account to check
     * @param blockNumber The block number to get the vote balance at
     * @return The number of votes the account had as of the given block
     */
    function getPriorVotes(address account, uint blockNumber)
        external
        view
        returns (uint256)
    {
        require(blockNumber < block.number, "YAM::getPriorVotes: not yet determined");

        uint32 nCheckpoints = numCheckpoints[account];
        if (nCheckpoints == 0) {
            return 0;
        }

        // First check most recent balance
        if (checkpoints[account][nCheckpoints - 1].fromBlock <= blockNumber) {
            return checkpoints[account][nCheckpoints - 1].votes;
        }

        // Next check implicit zero balance
        if (checkpoints[account][0].fromBlock > blockNumber) {
            return 0;
        }

        uint32 lower = 0;
        uint32 upper = nCheckpoints - 1;
        while (upper > lower) {
            uint32 center = upper - (upper - lower) / 2; // ceil, avoiding overflow
            Checkpoint memory cp = checkpoints[account][center];
            if (cp.fromBlock == blockNumber) {
                return cp.votes;
            } else if (cp.fromBlock < blockNumber) {
                lower = center;
            } else {
                upper = center - 1;
            }
        }
        return checkpoints[account][lower].votes;
    }

    function _delegate(address delegator, address delegatee)
        internal
    {
        address currentDelegate = _delegates[delegator];
        uint256 delegatorBalance = _yamBalances[delegator]; // balance of underlying YAMs (not scaled);
        _delegates[delegator] = delegatee;

        emit DelegateChanged(delegator, currentDelegate, delegatee);

        _moveDelegates(currentDelegate, delegatee, delegatorBalance);
    }

    function _moveDelegates(address srcRep, address dstRep, uint256 amount) internal {
        if (srcRep != dstRep && amount > 0) {
            if (srcRep != address(0)) {
                // decrease old representative
                uint32 srcRepNum = numCheckpoints[srcRep];
                uint256 srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;
                uint256 srcRepNew = srcRepOld.sub(amount);
                _writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
            }

            if (dstRep != address(0)) {
                // increase new representative
                uint32 dstRepNum = numCheckpoints[dstRep];
                uint256 dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;
                uint256 dstRepNew = dstRepOld.add(amount);
                _writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
            }
        }
    }

    function _writeCheckpoint(
        address delegatee,
        uint32 nCheckpoints,
        uint256 oldVotes,
        uint256 newVotes
    )
        internal
    {
        uint32 blockNumber = safe32(block.number, "YAM::_writeCheckpoint: block number exceeds 32 bits");

        if (nCheckpoints > 0 && checkpoints[delegatee][nCheckpoints - 1].fromBlock == blockNumber) {
            checkpoints[delegatee][nCheckpoints - 1].votes = newVotes;
        } else {
            checkpoints[delegatee][nCheckpoints] = Checkpoint(blockNumber, newVotes);
            numCheckpoints[delegatee] = nCheckpoints + 1;
        }

        emit DelegateVotesChanged(delegatee, oldVotes, newVotes);
    }

    function safe32(uint n, string memory errorMessage) internal pure returns (uint32) {
        require(n < 2**32, errorMessage);
        return uint32(n);
    }

    function getChainId() internal pure returns (uint) {
        uint256 chainId;
        assembly { chainId := chainid() }
        return chainId;
    }
}

contract YAMToken is YAMGovernanceToken {
    // Modifiers
    modifier onlyGov() {
        require(msg.sender == gov);
        _;
    }

    modifier onlyRebaser() {
        require(msg.sender == rebaser);
        _;
    }

    modifier onlyMinter() {
        require(
            msg.sender == rebaser
            || msg.sender == gov
            || msg.sender == incentivizer
            || msg.sender == migrator,
            "not minter"
        );
        _;
    }

    modifier validRecipient(address to) {
        require(to != address(0x0));
        require(to != address(this));
        _;
    }

    function initialize(
        string memory name_,
        string memory symbol_,
        uint8 decimals_
    )
        public
    {
        require(yamsScalingFactor == 0, "already initialized");
        name = name_;
        symbol = symbol_;
        decimals = decimals_;
    }


    /**
    * @notice Computes the current max scaling factor
    */
    function maxScalingFactor()
        external
        view
        returns (uint256)
    {
        return _maxScalingFactor();
    }

    function _maxScalingFactor()
        internal
        view
        returns (uint256)
    {
        // scaling factor can only go up to 2**256-1 = initSupply * yamsScalingFactor
        // this is used to check if yamsScalingFactor will be too high to compute balances when rebasing.
        return uint256(-1) / initSupply;
    }

    /**
    * @notice Mints new tokens, increasing totalSupply, initSupply, and a users balance.
    * @dev Limited to onlyMinter modifier
    */
    function mint(address to, uint256 amount)
        external
        onlyMinter
        returns (bool)
    {
        _mint(to, amount);
        return true;
    }

    function _mint(address to, uint256 amount)
        internal
    {
      if (msg.sender == migrator) {
        // migrator directly uses v2 balance for the amount

        // increase initSupply
        initSupply = initSupply.add(amount);

        // get external value
        uint256 scaledAmount = _yamToFragment(amount);

        // increase totalSupply
        totalSupply = totalSupply.add(scaledAmount);

        // make sure the mint didnt push maxScalingFactor too low
        require(yamsScalingFactor <= _maxScalingFactor(), "max scaling factor too low");

        // add balance
        _yamBalances[to] = _yamBalances[to].add(amount);

        // add delegates to the minter
        _moveDelegates(address(0), _delegates[to], amount);
        emit Mint(to, scaledAmount);
        emit Transfer(address(0), to, scaledAmount);
      } else {
        // increase totalSupply
        totalSupply = totalSupply.add(amount);

        // get underlying value
        uint256 yamValue = _fragmentToYam(amount);

        // increase initSupply
        initSupply = initSupply.add(yamValue);

        // make sure the mint didnt push maxScalingFactor too low
        require(yamsScalingFactor <= _maxScalingFactor(), "max scaling factor too low");

        // add balance
        _yamBalances[to] = _yamBalances[to].add(yamValue);

        // add delegates to the minter
        _moveDelegates(address(0), _delegates[to], yamValue);
        emit Mint(to, amount);
        emit Transfer(address(0), to, amount);
      }
    }

    /**
    * @notice Burns tokens from msg.sender, decreases totalSupply, initSupply, and a users balance.
    */

    function burn(uint256 amount)
        external
        returns (bool)
    {
        _burn(amount);
        return true;
    }

    function _burn(uint256 amount)
        internal
    {
                // decrease totalSupply
        totalSupply = totalSupply.sub(amount);

        // get underlying value
        uint256 yamValue = _fragmentToYam(amount);

        // decrease initSupply
        initSupply = initSupply.sub(yamValue);

        // decrease balance
        _yamBalances[msg.sender] = _yamBalances[msg.sender].sub(yamValue);

        // add delegates to the minter
        _moveDelegates(_delegates[msg.sender], address(0), yamValue);
        emit Burn(msg.sender, amount);
        emit Transfer(msg.sender, address(0), amount);
        }

    /**
    * @notice Mints new tokens using underlying amount, increasing totalSupply, initSupply, and a users balance.
    * @dev Limited to onlyMinter modifier
    */
    function mintUnderlying(address to, uint256 amount)
        external
        onlyMinter
        returns (bool)
    {
        _mintUnderlying(to, amount);
        return true;
    }

    function _mintUnderlying(address to, uint256 amount)
        internal
    {

        // increase initSupply
        initSupply = initSupply.add(amount);

        // get external value
        uint256 scaledAmount = _yamToFragment(amount);

        // increase totalSupply
        totalSupply = totalSupply.add(scaledAmount);

        // make sure the mint didnt push maxScalingFactor too low
        require(yamsScalingFactor <= _maxScalingFactor(), "max scaling factor too low");

        // add balance
        _yamBalances[to] = _yamBalances[to].add(amount);

        // add delegates to the minter
        _moveDelegates(address(0), _delegates[to], amount);
        emit Mint(to, scaledAmount);
        emit Transfer(address(0), to, scaledAmount);
   
    }

    /**
     * @dev Transfer underlying balance to a specified address.
     * @param to The address to transfer to.
     * @param value The amount to be transferred.
     * @return True on success, false otherwise.
     */
    function transferUnderlying(address to, uint256 value)
        external
        validRecipient(to)
        returns (bool)
    {
        // sub from balance of sender
        _yamBalances[msg.sender] = _yamBalances[msg.sender].sub(value);

        // add to balance of receiver
        _yamBalances[to] = _yamBalances[to].add(value);
        emit Transfer(msg.sender, to, _yamToFragment(value));

        _moveDelegates(_delegates[msg.sender], _delegates[to], value);
        return true;
    }
    
    /* - ERC20 functionality - */

    /**
    * @dev Transfer tokens to a specified address.
    * @param to The address to transfer to.
    * @param value The amount to be transferred.
    * @return True on success, false otherwise.
    */
    function transfer(address to, uint256 value)
        external
        validRecipient(to)
        returns (bool)
    {
        // underlying balance is stored in yams, so divide by current scaling factor

        // note, this means as scaling factor grows, dust will be untransferrable.
        // minimum transfer value == yamsScalingFactor / 1e24;

        // get amount in underlying
        uint256 yamValue = _fragmentToYam(value);

        // sub from balance of sender
        _yamBalances[msg.sender] = _yamBalances[msg.sender].sub(yamValue);

        // add to balance of receiver
        _yamBalances[to] = _yamBalances[to].add(yamValue);
        emit Transfer(msg.sender, to, value);

        _moveDelegates(_delegates[msg.sender], _delegates[to], yamValue);
        return true;
    }

    /**
    * @dev Transfer tokens from one address to another.
    * @param from The address you want to send tokens from.
    * @param to The address you want to transfer to.
    * @param value The amount of tokens to be transferred.
    */
    function transferFrom(address from, address to, uint256 value)
        external
        validRecipient(to)
        returns (bool)
    {
        // decrease allowance
        _allowedFragments[from][msg.sender] = _allowedFragments[from][msg.sender].sub(value);

        // get value in yams
        uint256 yamValue = _fragmentToYam(value);

        // sub from from
        _yamBalances[from] = _yamBalances[from].sub(yamValue);
        _yamBalances[to] = _yamBalances[to].add(yamValue);
        emit Transfer(from, to, value);

        _moveDelegates(_delegates[from], _delegates[to], yamValue);
        return true;
    }

    /**
    * @param who The address to query.
    * @return The balance of the specified address.
    */
    function balanceOf(address who)
      external
      view
      returns (uint256)
    {
      return _yamToFragment(_yamBalances[who]);
    }

    /** @notice Currently returns the internal storage amount
    * @param who The address to query.
    * @return The underlying balance of the specified address.
    */
    function balanceOfUnderlying(address who)
      external
      view
      returns (uint256)
    {
      return _yamBalances[who];
    }

    /**
     * @dev Function to check the amount of tokens that an owner has allowed to a spender.
     * @param owner_ The address which owns the funds.
     * @param spender The address which will spend the funds.
     * @return The number of tokens still available for the spender.
     */
    function allowance(address owner_, address spender)
        external
        view
        returns (uint256)
    {
        return _allowedFragments[owner_][spender];
    }

    /**
     * @dev Approve the passed address to spend the specified amount of tokens on behalf of
     * msg.sender. This method is included for ERC20 compatibility.
     * increaseAllowance and decreaseAllowance should be used instead.
     * Changing an allowance with this method brings the risk that someone may transfer both
     * the old and the new allowance - if they are both greater than zero - if a transfer
     * transaction is mined before the later approve() call is mined.
     *
     * @param spender The address which will spend the funds.
     * @param value The amount of tokens to be spent.
     */
    function approve(address spender, uint256 value)
        external
        returns (bool)
    {
        _allowedFragments[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
        return true;
    }

    /**
     * @dev Increase the amount of tokens that an owner has allowed to a spender.
     * This method should be used instead of approve() to avoid the double approval vulnerability
     * described above.
     * @param spender The address which will spend the funds.
     * @param addedValue The amount of tokens to increase the allowance by.
     */
    function increaseAllowance(address spender, uint256 addedValue)
        external
        returns (bool)
    {
        _allowedFragments[msg.sender][spender] =
            _allowedFragments[msg.sender][spender].add(addedValue);
        emit Approval(msg.sender, spender, _allowedFragments[msg.sender][spender]);
        return true;
    }

    /**
     * @dev Decrease the amount of tokens that an owner has allowed to a spender.
     *
     * @param spender The address which will spend the funds.
     * @param subtractedValue The amount of tokens to decrease the allowance by.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue)
        external
        returns (bool)
    {
        uint256 oldValue = _allowedFragments[msg.sender][spender];
        if (subtractedValue >= oldValue) {
            _allowedFragments[msg.sender][spender] = 0;
        } else {
            _allowedFragments[msg.sender][spender] = oldValue.sub(subtractedValue);
        }
        emit Approval(msg.sender, spender, _allowedFragments[msg.sender][spender]);
        return true;
    }

    // --- Approve by signature ---
    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    )
        external
    {
        require(now <= deadline, "YAM/permit-expired");

        bytes32 digest =
            keccak256(
                abi.encodePacked(
                    "\x19\x01",
                    DOMAIN_SEPARATOR,
                    keccak256(
                        abi.encode(
                            PERMIT_TYPEHASH,
                            owner,
                            spender,
                            value,
                            nonces[owner]++,
                            deadline
                        )
                    )
                )
            );

        require(owner != address(0), "YAM/invalid-address-0");
        require(owner == ecrecover(digest, v, r, s), "YAM/invalid-permit");
        _allowedFragments[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    /* - Governance Functions - */