Monte Finance Token & Staking - Smart Contract Audit Report

Summary

Monte Finance Audit Report The Monte Finance is building an innovative Defi platform that reduces supply via a Transaction Deflation Protocol, incentivises transactions and volume with a Transaction Fee Reward Mechanism and motivates holding via a Transaction Fee Staking Reward Contract.

We reviewed contracts provided to us by the team. When deployed to mainnet, we will verify the code and add the addresses here.


Notes on the Contracts:

    Token Contract:
  • The total supply of the token is 8,200.
  • There is a 3% tax on transfers of the token. The owner will choose when to enable the tax. Once enabled, it cannot be disabled.
  • These tokens are stored in the contract to provide rewards for users staking tokens.
  • The tokens from fees are sold on Uniswap to provide users to collect ETH, which is then sent to the staking pool and distributed (via shares) to stakers.
  • This sale and redistribution happens on all transfers that push the contract balance above a minimum amount that can be set by the team; meaning users may incur high gas fees on transfers.
  • The owner can update the tax fee at any time up to a hard-coded maximum of 10%
  • The owner can exclude any address from the transfer fee mechanism.
  • Utilization of SafeMath to prevent overflows.

  • Staking Contract:
  • Users can stake the project's token and to earn rewards in ETH.
  • Rewards are based upon the number of tokens staked in proportion to the staking pool and the amount of time the tokens have been staked for.
  • Users can stake and unstake their tokens at any time; and there are no fees.
  • Proper structuring of functions to avoid reentrancy issues.
  • Utilization of SafeMath to prevent overflows.

Audit Findings Summary:
  • No security issues from outside attackers were identified.
  • Ensure trust in the team as they can update the token address at any time.
  • Date: February 24th, 2021.
  • Update date: February 25th, 2021 - Ability to set the token address has been removed from the Staking contract along with other minor changes with no security implication.

Vulnerability CategoryNotesResult
Arbitrary Storage WriteN/APASS
Arbitrary JumpN/APASS
Delegate Call to Untrusted ContractN/APASS
Dependence on Predictable VariablesN/APASS
Deprecated OpcodesN/APASS
Ether ThiefN/APASS
ExceptionsN/APASS
External CallsN/APASS
Integer Over/UnderflowN/APASS
Multiple SendsN/APASS
SuicideN/APASS
State Change External CallsN/APass
Unchecked RetvalN/APASS
User Supplied AssertionN/APASS
Critical Solidity CompilerN/APASS
Overall Contract Safety PASS

Token Contract


Smart Contract Graph

Contract Inheritance


 ($) = payable function
 # = non-constant function
 
 Int = Internal
 Ext = External
 Pub = Public
 
 + [Lib] SafeMath 
    - [Int] tryAdd
    - [Int] trySub
    - [Int] tryMul
    - [Int] tryDiv
    - [Int] tryMod
    - [Int] add
    - [Int] sub
    - [Int] mul
    - [Int] div
    - [Int] mod
    - [Int] sub
    - [Int] div
    - [Int] mod

 +  Context 
    - [Int] _msgSender
    - [Int] _msgData

 +  Ownable (Context)
    - [Int]  #
    - [Pub] owner
    - [Pub] renounceOwnership #
       - modifiers: onlyOwner
    - [Pub] transferOwnership #
       - modifiers: onlyOwner

 + [Int] IERC20 
    - [Ext] totalSupply
    - [Ext] balanceOf
    - [Ext] transfer #
    - [Ext] allowance
    - [Ext] approve #
    - [Ext] transferFrom #

 +  ERC20 (Context, IERC20)
    - [Pub]  #
    - [Pub] name
    - [Pub] symbol
    - [Pub] decimals
    - [Pub] totalSupply
    - [Pub] balanceOf
    - [Pub] transfer #
    - [Pub] allowance
    - [Pub] approve #
    - [Pub] transferFrom #
    - [Pub] increaseAllowance #
    - [Pub] decreaseAllowance #
    - [Int] _transfer #
    - [Int] _mint #
    - [Int] _burn #
    - [Int] _approve #
    - [Int] _setupDecimals #
    - [Int] _beforeTokenTransfer #

 + [Int] IUniswapV2Factory 
    - [Ext] feeTo
    - [Ext] feeToSetter
    - [Ext] getPair
    - [Ext] allPairs
    - [Ext] allPairsLength
    - [Ext] createPair #
    - [Ext] setFeeTo #
    - [Ext] setFeeToSetter #

 + [Int] IUniswapV2Router01 
    - [Ext] factory
    - [Ext] WETH
    - [Ext] addLiquidity #
    - [Ext] addLiquidityETH ($)
    - [Ext] removeLiquidity #
    - [Ext] removeLiquidityETH #
    - [Ext] removeLiquidityWithPermit #
    - [Ext] removeLiquidityETHWithPermit #
    - [Ext] swapExactTokensForTokens #
    - [Ext] swapTokensForExactTokens #
    - [Ext] swapExactETHForTokens ($)
    - [Ext] swapTokensForExactETH #
    - [Ext] swapExactTokensForETH #
    - [Ext] swapETHForExactTokens ($)
    - [Ext] quote
    - [Ext] getAmountOut
    - [Ext] getAmountIn
    - [Ext] getAmountsOut
    - [Ext] getAmountsIn

 + [Int] IUniswapV2Router02 (IUniswapV2Router01)
    - [Ext] removeLiquidityETHSupportingFeeOnTransferTokens #
    - [Ext] removeLiquidityETHWithPermitSupportingFeeOnTransferTokens #
    - [Ext] swapExactTokensForTokensSupportingFeeOnTransferTokens #
    - [Ext] swapExactETHForTokensSupportingFeeOnTransferTokens ($)
    - [Ext] swapExactTokensForETHSupportingFeeOnTransferTokens #

 + [Int] IStaking 
    - [Ext] distribute ($)

 +  Monte (Context, Ownable, ERC20)
    - [Pub]  #
       - modifiers: ERC20
    - [Ext] setTaxActive #
       - modifiers: onlyOwner
    - [Ext] setTaxless #
       - modifiers: onlyOwner
    - [Ext] setTaxFee #
       - modifiers: onlyOwner
    - [Ext] setStakingPool #
       - modifiers: onlyOwner
    - [Ext] setSwapEnabled #
       - modifiers: onlyOwner
    - [Ext] setMinTokenBeforeSwap #
       - modifiers: onlyOwner
    - [Pub] transferFrom #
    - [Int] _transfer #
    - [Prv] swapAndDistribute #
       - modifiers: lockTheSwap
    - [Ext]  ($)
							

Click here to download the source code as a .sol file.


// 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: node_modules\@openzeppelin\contracts\utils\Context.solpragma solidity >=0.6.0 <0.8.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

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

// File: @openzeppelin\contracts\access\Ownable.solpragma solidity >=0.6.0 <0.8.0;

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

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

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

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

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

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

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: node_modules\@openzeppelin\contracts\token\ERC20\IERC20.solpragma 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\token\ERC20\ERC20.sol

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name_, string memory symbol_) public {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal virtual {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

// File: contracts\uniswap\IUniswapV2Factory.solpragma solidity >=0.6.0;

interface IUniswapV2Factory {
    event PairCreated(address indexed token0, address indexed token1, address pair, uint);

    function feeTo() external view returns (address);
    function feeToSetter() external view returns (address);

    function getPair(address tokenA, address tokenB) external view returns (address pair);
    function allPairs(uint) external view returns (address pair);
    function allPairsLength() external view returns (uint);

    function createPair(address tokenA, address tokenB) external returns (address pair);

    function setFeeTo(address) external;
    function setFeeToSetter(address) external;
}

// File: contracts\uniswap\IUniswapV2Router01.solpragma solidity >=0.6.2;

interface IUniswapV2Router01 {
    function factory() external pure returns (address);
    function WETH() external pure returns (address);

    function addLiquidity(
        address tokenA,
        address tokenB,
        uint amountADesired,
        uint amountBDesired,
        uint amountAMin,
        uint amountBMin,
        address to,
        uint deadline
    ) external returns (uint amountA, uint amountB, uint liquidity);
    function addLiquidityETH(
        address token,
        uint amountTokenDesired,
        uint amountTokenMin,
        uint amountETHMin,
        address to,
        uint deadline
    ) external payable returns (uint amountToken, uint amountETH, uint liquidity);
    function removeLiquidity(
        address tokenA,
        address tokenB,
        uint liquidity,
        uint amountAMin,
        uint amountBMin,
        address to,
        uint deadline
    ) external returns (uint amountA, uint amountB);
    function removeLiquidityETH(
        address token,
        uint liquidity,
        uint amountTokenMin,
        uint amountETHMin,
        address to,
        uint deadline
    ) external returns (uint amountToken, uint amountETH);
    function removeLiquidityWithPermit(
        address tokenA,
        address tokenB,
        uint liquidity,
        uint amountAMin,
        uint amountBMin,
        address to,
        uint deadline,
        bool approveMax, uint8 v, bytes32 r, bytes32 s
    ) external returns (uint amountA, uint amountB);
    function removeLiquidityETHWithPermit(
        address token,
        uint liquidity,
        uint amountTokenMin,
        uint amountETHMin,
        address to,
        uint deadline,
        bool approveMax, uint8 v, bytes32 r, bytes32 s
    ) external returns (uint amountToken, uint amountETH);
    function swapExactTokensForTokens(
        uint amountIn,
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
    ) external returns (uint[] memory amounts);
    function swapTokensForExactTokens(
        uint amountOut,
        uint amountInMax,
        address[] calldata path,
        address to,
        uint deadline
    ) external returns (uint[] memory amounts);
    function swapExactETHForTokens(uint amountOutMin, address[] calldata path, address to, uint deadline)
        external
        payable
        returns (uint[] memory amounts);
    function swapTokensForExactETH(uint amountOut, uint amountInMax, address[] calldata path, address to, uint deadline)
        external
        returns (uint[] memory amounts);
    function swapExactTokensForETH(uint amountIn, uint amountOutMin, address[] calldata path, address to, uint deadline)
        external
        returns (uint[] memory amounts);
    function swapETHForExactTokens(uint amountOut, address[] calldata path, address to, uint deadline)
        external
        payable
        returns (uint[] memory amounts);

    function quote(uint amountA, uint reserveA, uint reserveB) external pure returns (uint amountB);
    function getAmountOut(uint amountIn, uint reserveIn, uint reserveOut) external pure returns (uint amountOut);
    function getAmountIn(uint amountOut, uint reserveIn, uint reserveOut) external pure returns (uint amountIn);
    function getAmountsOut(uint amountIn, address[] calldata path) external view returns (uint[] memory amounts);
    function getAmountsIn(uint amountOut, address[] calldata path) external view returns (uint[] memory amounts);
}

// File: contracts\uniswap\IUniswapV2Router02.solpragma solidity >=0.6.2;interface IUniswapV2Router02 is IUniswapV2Router01 {
    function removeLiquidityETHSupportingFeeOnTransferTokens(
        address token,
        uint liquidity,
        uint amountTokenMin,
        uint amountETHMin,
        address to,
        uint deadline
    ) external returns (uint amountETH);
    function removeLiquidityETHWithPermitSupportingFeeOnTransferTokens(
        address token,
        uint liquidity,
        uint amountTokenMin,
        uint amountETHMin,
        address to,
        uint deadline,
        bool approveMax, uint8 v, bytes32 r, bytes32 s
    ) external returns (uint amountETH);

    function swapExactTokensForTokensSupportingFeeOnTransferTokens(
        uint amountIn,
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
    ) external;
    function swapExactETHForTokensSupportingFeeOnTransferTokens(
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
    ) external payable;
    function swapExactTokensForETHSupportingFeeOnTransferTokens(
        uint amountIn,
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
    ) external;
}

// File: contracts\IStaking.solpragma solidity ^0.6.0;

interface IStaking {
    function distribute() external payable;
}

// File: contracts\Monte.solpragma solidity ^0.6.0;

contract Monte is Context, Ownable, ERC20 {
    using SafeMath for uint256;
    
    IUniswapV2Router02 public  uniswapV2Router;
    address public  uniswapV2Pair;

    address public stakingPool;
    uint256 public taxFee = 300;
    uint256 public taxFeeTotal;

    bool public isTaxActive = true;
    mapping(address => bool) public isTaxless;

    uint256 public minTokenBeforeSwap = 1000e18;
    bool private inSwap;
    bool public isSwapEnabled = false;
    
    uint256 public totalEthDistributed;

    event SwapedTokenForEth(uint256 ethAmount, uint256 tokenAmount);

    modifier lockTheSwap {
        inSwap = true;
        _;
        inSwap = false;
    }

    constructor() ERC20("Monte.finance","MNT") public {
        uniswapV2Router = IUniswapV2Router02(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D);
        uniswapV2Pair = IUniswapV2Factory(uniswapV2Router.factory())
            .createPair(address(this), uniswapV2Router.WETH());
        _mint(_msgSender(),10_000_000e18);
        isTaxless[address(this)] = true;
        isTaxless[_msgSender()] = true;
    }

    function setTaxActive(bool _value) external onlyOwner {
        isTaxActive = _value;
    }

    function setTaxless(address account, bool _value) external onlyOwner {
        isTaxless[account] = _value;
    }

    function setTaxFee(uint256 _taxFee) external onlyOwner {
        require(_taxFee > 0 && _taxFee <= 10, "MNT: Tax Fee out of range!");
        taxFee = _taxFee;
    }

    function setStakingPool(address _stakingPool) external onlyOwner {
        isTaxless[stakingPool] = false;
        isTaxless[_stakingPool] = true;
        stakingPool = _stakingPool;
    }
    
    function setSwapEnabled(bool _value) external onlyOwner {
        isSwapEnabled = _value;
    }
    
    function setMinTokenBeforeSwap(uint256 amount) external onlyOwner {
        minTokenBeforeSwap = amount;
    }
    
    function transferFrom(address sender, address recipient, uint amount) public override returns (bool) {
        _transfer(sender, recipient, amount);
        if(_msgSender() == stakingPool) return true;

        _approve(sender, _msgSender(), allowance(sender,_msgSender()).sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    function _transfer(address sender, address recipient, uint256 amount) internal override {
        if(isSwapEnabled && !inSwap && sender != uniswapV2Pair){
            swapAndDistribute();
        }
        uint256 transferAmount = amount;
        if(isTaxActive && !isTaxless[sender] && !isTaxless[recipient]) {
            uint256 fee = amount.mul(taxFee).div(10_000);
            super._transfer(sender,address(this),fee);
            transferAmount = amount.sub(fee);
            taxFeeTotal = taxFeeTotal.add(fee);
        }
        super._transfer(sender, recipient, transferAmount);
    }
  
    function swapAndDistribute() private lockTheSwap {
        uint256 tokenAmount = balanceOf(address(this));
        if(tokenAmount < minTokenBeforeSwap) return;

        uint256 ethAmount = address(this).balance;
        
        address[] memory path = new address[](2);
        path[0] = address(this);
        path[1] = uniswapV2Router.WETH();

        _approve(address(this), address(uniswapV2Router), tokenAmount);

        uniswapV2Router.swapExactTokensForETHSupportingFeeOnTransferTokens(
            tokenAmount,
            0,
            path,
            address(this),
            block.timestamp
        );
        
        ethAmount = address(this).balance.sub(ethAmount);
        emit SwapedTokenForEth(tokenAmount,ethAmount);
        
        uint256 amountToDistribute = address(this).balance;
        totalEthDistributed = totalEthDistributed.add(amountToDistribute);
        IStaking(stakingPool).distribute{value: amountToDistribute}();
    }
    
    receive() external payable {}
}


Staking Contract


Smart Contract Graph

Contract Inheritance


 ($) = payable function
 # = non-constant function
 
 Int = Internal
 Ext = External
 Pub = Public
 
 + [Lib] SafeMath 
    - [Int] add
    - [Int] sub
    - [Int] sub
    - [Int] mul
    - [Int] div
    - [Int] div
    - [Int] mod
    - [Int] mod

 +  Context 
    - [Int]  #
    - [Int] _msgSender
    - [Int] _msgData

 +  Ownable (Context)
    - [Int]  #
    - [Pub] owner
    - [Pub] renounceOwnership #
       - modifiers: onlyOwner
    - [Pub] transferOwnership #
       - modifiers: onlyOwner

 + [Lib] BasisPoints 
    - [Int] mulBP
    - [Int] divBP
    - [Int] addBP
    - [Int] subBP

 + [Int] IERC20 
    - [Ext] transfer #
    - [Ext] approve #
    - [Ext] transferFrom #
    - [Ext] allowance
    - [Ext] totalSupply
    - [Ext] balanceOf

 +  Staking (Context, Ownable)
    - [Pub]  #
    - [Pub] setToken #
       - modifiers: onlyOwner
    - [Ext] setStartTime #
       - modifiers: onlyOwner
    - [Pub] stake #
       - modifiers: whenStakingActive
    - [Ext] unstake #
       - modifiers: whenStakingActive
    - [Pub] withdraw #
       - modifiers: whenStakingActive
    - [Ext] distribute ($)
    - [Pub] dividendsOf
    - [Pub] totalStakedAt
    - [Pub] stakeValueAt
    - [Int] uintToInt
    - [Int] _addStake #
    - [Int] _increaseProfitPerShare #
    - [Int] _getCheckpointValueAt
    - [Int] _updateCheckpointValueAtNow #

							

Click here to download the source code as a .sol file.



// SPDX-License-Identifier: MIT

pragma solidity ^0.5.16;

library SafeMath {
   
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }
   
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    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;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

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

        return c;
    }

    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

contract Context {
    
    constructor () internal { }

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

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

contract Ownable is Context {
    address private _owner;
    event OwnershipTransferred(
        address indexed previousOwner,
        address indexed newOwner
    );
    constructor() internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }
    function owner() public view returns (address) {
        return _owner;
    }
    modifier onlyOwner() {
        require(_owner == _msgSender(), "Ownable: caller is not the owner");
        _;
    }
    function renounceOwnership() public  onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }
    function transferOwnership(address newOwner) public onlyOwner {
        require(
            newOwner != address(0),
            "Ownable: new owner is the zero address"
        );
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

library BasisPoints {
    using SafeMath for uint;

    uint constant private BASIS_POINTS = 10000;

    function mulBP(uint amt, uint bp) internal pure returns (uint) {
        if (amt == 0) return 0;
        return amt.mul(bp).div(BASIS_POINTS);
    }

    function divBP(uint amt, uint bp) internal pure returns (uint) {
        require(bp > 0, "Cannot divide by zero.");
        if (amt == 0) return 0;
        return amt.mul(BASIS_POINTS).div(bp);
    }

    function addBP(uint amt, uint bp) internal pure returns (uint) {
        if (amt == 0) return 0;
        if (bp == 0) return amt;
        return amt.add(mulBP(amt, bp));
    }

    function subBP(uint amt, uint bp) internal pure returns (uint) {
        if (amt == 0) return 0;
        if (bp == 0) return amt;
        return amt.sub(mulBP(amt, bp));
    }
}

interface IERC20 {
    function transfer(address recipient, uint256 amount) external returns (bool);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract Staking is Context, Ownable {
    using BasisPoints for uint;
    using SafeMath for uint;

    uint256 constant internal DISTRIBUTION_MULTIPLIER = 2 ** 64;

    IERC20 private token;

    mapping(address => uint) public stakeValue;
    mapping(address => int) public stakerPayouts;

    uint public totalDistributions;
    uint public totalStaked;
    uint public totalStakers;
    uint public profitPerShare;
    uint private emptyStakeTokens; //These are eth given to the contract when there are no stakers.

    uint public startTime;

    event OnDistribute(address sender, uint amountSent);
    event OnStake(address sender, uint amount);
    event OnUnstake(address sender, uint amount);
    event OnReinvest(address sender, uint amount);
    event OnWithdraw(address sender, uint amount);

    struct Checkpoint {
      uint128 fromBlock;
      uint128 value;
    }

    mapping(address => Checkpoint[]) internal stakeValueHistory;

    Checkpoint[] internal totalStakedHistory;

    modifier whenStakingActive {
        require(startTime != 0 && now > startTime, "Staking not yet started.");
        _;
    }

    constructor(IERC20 _token) public {
        token = _token;
    }

    function setToken(IERC20 _token) public onlyOwner {
        token = _token;
        startTime = block.timestamp;
    }

    function setStartTime(uint _startTime) external onlyOwner {
        startTime = _startTime;
    }

    function stake(uint amount) public whenStakingActive {
        require(token.balanceOf(msg.sender) >= amount, "Cannot stake more Tokens than you hold unstaked.");
        if (stakeValue[msg.sender] == 0) totalStakers = totalStakers.add(1);
        _addStake(amount);
        require(token.transferFrom(msg.sender, address(this), amount), "Stake failed due to failed transfer.");
        emit OnStake(msg.sender, amount);
    }

    function unstake(uint amount) external whenStakingActive {
        require(stakeValue[msg.sender] >= amount, "Cannot unstake more Token than you have staked.");
        // Update staker's history
        _updateCheckpointValueAtNow(
        stakeValueHistory[msg.sender],
        stakeValue[msg.sender],
        stakeValue[msg.sender].sub(amount)
        );

        // Update total staked history
        _updateCheckpointValueAtNow(
        totalStakedHistory,
        totalStaked,
        totalStaked.sub(amount)
        );
        
        //must withdraw all dividends, to prevent overflows
        withdraw(dividendsOf(msg.sender));
        if (stakeValue[msg.sender] == amount) totalStakers = totalStakers.sub(1);
        totalStaked = totalStaked.sub(amount);
        stakeValue[msg.sender] = stakeValue[msg.sender].sub(amount);

        stakerPayouts[msg.sender] = uintToInt(profitPerShare.mul(stakeValue[msg.sender]));
        
        require(token.transferFrom(address(this), msg.sender, amount), "Unstake failed due to failed transfer.");
        emit OnUnstake(msg.sender, amount);
    }

    function withdraw(uint amount) public whenStakingActive {
        require(dividendsOf(msg.sender) >= amount, "Cannot withdraw more dividends than you have earned.");
        stakerPayouts[msg.sender] = stakerPayouts[msg.sender] + uintToInt(amount.mul(DISTRIBUTION_MULTIPLIER));
        msg.sender.transfer(amount);
        emit OnWithdraw(msg.sender, amount);
    }

    function distribute() external payable {
        uint amount = msg.value;
        if(amount > 0){
            totalDistributions = totalDistributions.add(amount);
            _increaseProfitPerShare(amount);
            emit OnDistribute(msg.sender, amount);
        }
    }

    function dividendsOf(address staker) public view returns (uint) {
        int divPayout = uintToInt(profitPerShare.mul(stakeValue[staker]));
        require(divPayout >= stakerPayouts[staker], "dividend calc overflow");
        return uint(divPayout - stakerPayouts[staker])
            .div(DISTRIBUTION_MULTIPLIER);
    }

    function totalStakedAt(uint _blockNumber) public view returns(uint) {
        // If we haven't initialized history yet
        if (totalStakedHistory.length == 0) {
            // Use the existing value
            return totalStaked;
        } else {
            // Binary search history for the proper staked amount
            return _getCheckpointValueAt(
                totalStakedHistory,
                _blockNumber
            );
        }
    }

    function stakeValueAt(address _owner, uint _blockNumber) public view returns (uint) {
        // If we haven't initialized history yet
        if (stakeValueHistory[_owner].length == 0) {
            // Use the existing latest value
            return stakeValue[_owner];
        } else {
            // Binary search history for the proper staked amount
            return _getCheckpointValueAt(stakeValueHistory[_owner], _blockNumber);
        }
    }

    function uintToInt(uint val) internal pure returns (int) {
        if (val >= uint(-1).div(2)) {
            require(false, "Overflow. Cannot convert uint to int.");
        } else {
            return int(val);
        }
    }

    function _addStake(uint _amount) internal {
        // Update staker's history
        _updateCheckpointValueAtNow(
        stakeValueHistory[msg.sender],
        stakeValue[msg.sender],
        stakeValue[msg.sender].add(_amount)
        );

        // Update total staked history
        _updateCheckpointValueAtNow(
        totalStakedHistory,
        totalStaked,
        totalStaked.add(_amount)
        );

        totalStaked = totalStaked.add(_amount);
        stakeValue[msg.sender] = stakeValue[msg.sender].add(_amount);
        
        uint payout = profitPerShare.mul(_amount);
        stakerPayouts[msg.sender] = stakerPayouts[msg.sender] + uintToInt(payout);
    }

    function _increaseProfitPerShare(uint amount) internal {
        if (totalStaked != 0) {
            if (emptyStakeTokens != 0) {
                amount = amount.add(emptyStakeTokens);
                emptyStakeTokens = 0;
            }
            profitPerShare = profitPerShare.add(amount.mul(DISTRIBUTION_MULTIPLIER).div(totalStaked));
        } else {
            emptyStakeTokens = emptyStakeTokens.add(amount);
        }
    }

    function _getCheckpointValueAt(Checkpoint[] storage checkpoints, uint _block) view internal returns (uint) {
    // This case should be handled by caller
    if (checkpoints.length == 0)
      return 0;

    // Use the latest checkpoint
    if (_block >= checkpoints[checkpoints.length-1].fromBlock)
      return checkpoints[checkpoints.length-1].value;

    // Use the oldest checkpoint
    if (_block < checkpoints[0].fromBlock)
      return checkpoints[0].value;

    // Binary search of the value in the array
    uint min = 0;
    uint max = checkpoints.length-1;
    while (max > min) {
      uint mid = (max + min + 1) / 2;
      if (checkpoints[mid].fromBlock<=_block) {
        min = mid;
      } else {
        max = mid-1;
      }
    }
    return checkpoints[min].value;
  }

  function _updateCheckpointValueAtNow(
    Checkpoint[] storage checkpoints,
    uint _oldValue,
    uint _value
  ) internal {
    require(_value <= uint128(-1));
    require(_oldValue <= uint128(-1));

    if (checkpoints.length == 0) {
      Checkpoint storage genesis = checkpoints[checkpoints.length++];
      genesis.fromBlock = uint128(block.number - 1);
      genesis.value = uint128(_oldValue);
    }

    if (checkpoints[checkpoints.length - 1].fromBlock < block.number) {
      Checkpoint storage newCheckPoint = checkpoints[checkpoints.length++];
      newCheckPoint.fromBlock = uint128(block.number);
      newCheckPoint.value = uint128(_value);
    } else {
      Checkpoint storage oldCheckPoint = checkpoints[checkpoints.length - 1];
      oldCheckPoint.value = uint128(_value);
    }
  }
  
}