The gh from godhunter97

Pancake

/**
*Submitted for verification at BscScan.com on 2020-10-30
*/

@dev Provides information about the current execution context, including the
sender of the transaction and its data. While these are generally available
via msg.sender and msg.data, they should not be accessed in such a direct
manner, since when dealing with GSN meta-transactions the account sending and
paying for execution may not be the actual sender (as far as an application
is concerned).
This contract is only required for intermediate, library-like contracts.
*/
contract Context {
// Empty internal constructor, to prevent people from mistakenly deploying
// an instance of this contract, which should be used via inheritance.
constructor() internal {}

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 ethereum/solidity#2691
return msg.data;
}
}

/**

@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.
*/
contract Ownable is Context {
address private _owner;

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

/**
- @dev Initializes the contract setting the deployer as the initial owner.
  */
  constructor() internal {
  address msgSender = _msgSender();
  _owner = msgSender;
  emit OwnershipTransferred(address(0), msgSender);
  }
/**
- @dev Returns the address of the current owner.
  */
  function owner() public view returns (address) {
  return _owner;
  }
/**
- @dev Throws if called by any account other than the owner.
  */
  modifier onlyOwner() {
  require(_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 onlyOwner {
  emit OwnershipTransferred(_owner, address(0));
  _owner = address(0);
  }
/**
- @dev Transfers ownership of the contract to a new account (newOwner).
- Can only be called by the current owner.
  */
  function transferOwnership(address newOwner) public onlyOwner {
  _transferOwnership(newOwner);
  }
/**
- @dev Transfers ownership of the contract to a new account (newOwner).
  */
  function _transferOwnership(address newOwner) internal {
  require(newOwner != address(0), 'Ownable: new owner is the zero address');
  emit OwnershipTransferred(_owner, newOwner);
  _owner = newOwner;
  }
  }

interface IBEP20 {
/**
* @dev Returns the amount of tokens in existence.
*/
function totalSupply() external view returns (uint256);

/**
 * @dev Returns the token decimals.
 */
function decimals() external view returns (uint8);

/**
 * @dev Returns the token symbol.
 */
function symbol() external view returns (string memory);

/**
 * @dev Returns the token name.
 */
function name() external view returns (string memory);

/**
 * @dev Returns the bep token owner.
 */
function getOwner() external view returns (address);

/**
 * @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);

}

/**

@dev Wrappers over Solidity's arithmetic operations with added overflow
checks.
Arithmetic operations in Solidity wrap on overflow. This can easily result
in bugs, because programmers usually assume that an overflow raises an
error, which is the standard behavior in high level programming languages.
SafeMath restores this intuition by reverting the transaction when an
operation overflows.
Using this library instead of the unchecked operations eliminates an entire
class of bugs, so it's recommended to use it always.
/
library SafeMath {
/*
- @dev Returns the addition of two unsigned integers, reverting on
- overflow.
- Counterpart to Solidity's + operator.
- Requirements:
- - Addition cannot overflow.
    */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a, 'SafeMath: addition overflow');
  return c;
  }
/**
- @dev Returns the subtraction of two unsigned integers, reverting on
- overflow (when the result is negative).
- Counterpart to Solidity's - operator.
- Requirements:
- - Subtraction cannot overflow.
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    return sub(a, b, 'SafeMath: subtraction overflow');
    }
/**
- @dev Returns the subtraction of two unsigned integers, reverting with custom message on
- overflow (when the result is negative).
- Counterpart to Solidity's - operator.
- Requirements:
- - Subtraction cannot overflow.
    */
    function sub(
    uint256 a,
    uint256 b,
    string memory errorMessage
    ) internal pure returns (uint256) {
    require(b <= a, errorMessage);
    uint256 c = a - b;
  return c;
  }
/**
- @dev Returns the multiplication of two unsigned integers, reverting on
- overflow.
- Counterpart to Solidity's * operator.
- Requirements:
- - Multiplication cannot overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: OpenZeppelin/openzeppelin-contracts#522
    if (a == 0) {
    return 0;
    }
  uint256 c = a * b;
  require(c / a == b, 'SafeMath: multiplication overflow');
  
  return c;
  }
/**
- @dev Returns the integer division of two unsigned integers. Reverts on
- division by zero. The result is rounded towards zero.
- Counterpart to Solidity's / operator. Note: this function uses a
- revert opcode (which leaves remaining gas untouched) while Solidity
- uses an invalid opcode to revert (consuming all remaining gas).
- Requirements:
- - The divisor cannot be zero.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
    return div(a, b, 'SafeMath: division by zero');
    }
/**
- @dev Returns the integer division of two unsigned integers. Reverts with custom message on
- division by zero. The result is rounded towards zero.
- Counterpart to Solidity's / operator. Note: this function uses a
- revert opcode (which leaves remaining gas untouched) while Solidity
- uses an invalid opcode to revert (consuming all remaining gas).
- Requirements:
- - The divisor cannot be zero.
    */
    function div(
    uint256 a,
    uint256 b,
    string memory errorMessage
    ) internal pure returns (uint256) {
    require(b > 0, errorMessage);
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
  return c;
  }
/**
- @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
- Reverts when dividing by zero.
- Counterpart to Solidity's % operator. This function uses a revert
- opcode (which leaves remaining gas untouched) while Solidity uses an
- invalid opcode to revert (consuming all remaining gas).
- Requirements:
- - The divisor cannot be zero.
    */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    return mod(a, b, 'SafeMath: modulo by zero');
    }
/**
- @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
- Reverts with custom message when dividing by zero.
- Counterpart to Solidity's % operator. This function uses a revert
- opcode (which leaves remaining gas untouched) while Solidity uses an
- invalid opcode to revert (consuming all remaining gas).
- Requirements:
- - The divisor cannot be zero.
    */
    function mod(
    uint256 a,
    uint256 b,
    string memory errorMessage
    ) internal pure returns (uint256) {
    require(b != 0, errorMessage);
    return a % b;
    }
function min(uint256 x, uint256 y) internal pure returns (uint256 z) {
z = x < y ? x : y;
}

// babylonian method (https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Babylonian_method)
function sqrt(uint256 y) internal pure returns (uint256 z) {
if (y > 3) {
z = y;
uint256 x = y / 2 + 1;
while (x < z) {
z = x;
x = (y / x + x) / 2;
}
} else if (y != 0) {
z = 1;
}
}
}

/**

@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) {
  // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
  // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
  // for accounts without code, i.e. keccak256('')
  bytes32 codehash;
  bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
  // solhint-disable-next-line no-inline-assembly
  assembly {
  codehash := extcodehash(account)
  }
  return (codehash != accountHash && codehash != 0x0);
  }
/**
- @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
- plaincall 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');
  return _functionCallWithValue(target, data, value, errorMessage);
  }
function _functionCallWithValue(
address target,
bytes memory data,
uint256 weiValue,
string memory errorMessage
) private returns (bytes memory) {
require(isContract(target), 'Address: call to non-contract');
```
 // solhint-disable-next-line avoid-low-level-calls
 (bool success, bytes memory returndata) = target.call{value: weiValue}(data);
 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);
     }
 }
```
}
}

/**

@dev Implementation of the {IBEP20} 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 {BEP20PresetMinterPauser}.
TIP: For a detailed writeup see our guide
https://forum.zeppelin.solutions/t/how-to-implement-BEP20-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 BEP20 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 {IBEP20-approve}.
*/
contract BEP20 is Context, IBEP20, Ownable {
using SafeMath for uint256;
using Address for address;

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 bep token owner.
  */
  function getOwner() external override view returns (address) {
  return owner();
  }
/**
- @dev Returns the token name.
  */
  function name() public override view returns (string memory) {
  return _name;
  }
/**
- @dev Returns the token decimals.
  */
  function decimals() public override view returns (uint8) {
  return _decimals;
  }
/**
- @dev Returns the token symbol.
  */
  function symbol() public override view returns (string memory) {
  return _symbol;
  }
/**
- @dev See {BEP20-totalSupply}.
  */
  function totalSupply() public override view returns (uint256) {
  return _totalSupply;
  }
/**
- @dev See {BEP20-balanceOf}.
  */
  function balanceOf(address account) public override view returns (uint256) {
  return _balances[account];
  }
/**
- @dev See {BEP20-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 override returns (bool) {
    _transfer(_msgSender(), recipient, amount);
    return true;
    }
/**
- @dev See {BEP20-allowance}.
  */
  function allowance(address owner, address spender) public override view returns (uint256) {
  return _allowances[owner][spender];
  }
/**
- @dev See {BEP20-approve}.
- Requirements:
- - spender cannot be the zero address.
    */
    function approve(address spender, uint256 amount) public override returns (bool) {
    _approve(_msgSender(), spender, amount);
    return true;
    }
/**
- @dev See {BEP20-transferFrom}.
- Emits an {Approval} event indicating the updated allowance. This is not
- required by the EIP. See the note at the beginning of {BEP20};
- 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 override returns (bool) {
  _transfer(sender, recipient, amount);
  _approve(
  sender,
  _msgSender(),
  _allowances[sender][_msgSender()].sub(amount, 'BEP20: 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 {BEP20-approve}.
- Emits an {Approval} event indicating the updated allowance.
- Requirements:
- - spender cannot be the zero address.
    */
    function increaseAllowance(address spender, uint256 addedValue) public 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 {BEP20-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 returns (bool) {
  _approve(
  _msgSender(),
  spender,
  _allowances[_msgSender()][spender].sub(subtractedValue, 'BEP20: decreased allowance below zero')
  );
  return true;
  }
/**
- @dev Creates amount tokens and assigns them to msg.sender, increasing
- the total supply.
- Requirements
- - msg.sender must be the token owner
    */
    function mint(uint256 amount) public onlyOwner returns (bool) {
    _mint(_msgSender(), amount);
    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 {
    require(sender != address(0), 'BEP20: transfer from the zero address');
    require(recipient != address(0), 'BEP20: transfer to the zero address');
  _balances[sender] = _balances[sender].sub(amount, 'BEP20: 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 {
    require(account != address(0), 'BEP20: mint to the zero address');
  _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 {
    require(account != address(0), 'BEP20: burn from the zero address');
  _balances[account] = _balances[account].sub(amount, 'BEP20: burn amount exceeds balance');
  _totalSupply = _totalSupply.sub(amount);
  emit Transfer(account, address(0), amount);
  }
/**
- @dev Sets amount as the allowance of spender over the owners tokens.
- This is 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 {
    require(owner != address(0), 'BEP20: approve from the zero address');
    require(spender != address(0), 'BEP20: approve to the zero address');
  _allowances[owner][spender] = amount;
  emit Approval(owner, spender, amount);
  }
/**
- @dev Destroys amount tokens from account.amount is then deducted
- from the caller's allowance.
- See {_burn} and {_approve}.
  */
  function _burnFrom(address account, uint256 amount) internal {
  _burn(account, amount);
  _approve(
  account,
  _msgSender(),
  _allowances[account][_msgSender()].sub(amount, 'BEP20: burn amount exceeds allowance')
  );
  }
  }

| _ )_ _ _ _ _ _ _ _ | | | |
| _ \ || | ' | ' \ || | || ||
|/_,||||||_, | () ()
|__/

MIT License
===========
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
*/

// BunnyToken with Governance.
contract BunnyToken is BEP20('Bunny Token', 'BUNNY') {
/// @notice Creates _amount token to _to. Must only be called by the owner (MasterChef).
function mint(address _to, uint256 _amount) public onlyOwner {
_mint(_to, _amount);
_moveDelegates(address(0), _delegates[_to], _amount);
}

// Copied and modified from YAM code:
// https://github.com/yam-finance/yam-protocol/blob/master/contracts/token/YAMGovernanceStorage.sol
// https://github.com/yam-finance/yam-protocol/blob/master/contracts/token/YAMGovernance.sol
// Which is copied and modified from COMPOUND:
// https://github.com/compound-finance/compound-protocol/blob/master/contracts/Governance/Comp.sol

/// @notice A record of each accounts delegate
mapping (address => address) internal _delegates;

/// @notice A checkpoint for marking number of votes from a given block
struct Checkpoint {
    uint32 fromBlock;
    uint256 votes;
}

/// @notice A record of votes checkpoints for each account, by index
mapping (address => mapping (uint32 => Checkpoint)) public checkpoints;

/// @notice The number of checkpoints for each account
mapping (address => uint32) public numCheckpoints;

/// @notice The EIP-712 typehash for the contract's domain
bytes32 public constant DOMAIN_TYPEHASH = keccak256("EIP712Domain(string name,uint256 chainId,address verifyingContract)");

/// @notice The EIP-712 typehash for the delegation struct used by the contract
bytes32 public constant DELEGATION_TYPEHASH = keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");

/// @notice A record of states for signing / validating signatures
mapping (address => uint) public nonces;

/// @notice An event thats emitted when an account changes its delegate
event DelegateChanged(address indexed delegator, address indexed fromDelegate, address indexed toDelegate);

/// @notice An event thats emitted when a delegate account's vote balance changes
event DelegateVotesChanged(address indexed delegate, uint previousBalance, uint newBalance);

/**
 * @notice Delegate votes from `msg.sender` to `delegatee`
 * @param delegator The address to get delegatee for
 */
function delegates(address delegator)
external
view
returns (address)
{
    return _delegates[delegator];
}

/**
 * @notice Delegate votes from `msg.sender` to `delegatee`
 * @param delegatee The address to delegate votes to
 */
function delegate(address delegatee) external {
    return _delegate(msg.sender, delegatee);
}

/**
 * @notice Delegates votes from signatory to `delegatee`
 * @param delegatee The address to delegate votes to
 * @param nonce The contract state required to match the signature
 * @param expiry The time at which to expire the signature
 * @param v The recovery byte of the signature
 * @param r Half of the ECDSA signature pair
 * @param s Half of the ECDSA signature pair
 */
function delegateBySig(
    address delegatee,
    uint nonce,
    uint expiry,
    uint8 v,
    bytes32 r,
    bytes32 s
)
external
{
    bytes32 domainSeparator = keccak256(
        abi.encode(
            DOMAIN_TYPEHASH,
            keccak256(bytes(name())),
            getChainId(),
            address(this)
        )
    );

    bytes32 structHash = keccak256(
        abi.encode(
            DELEGATION_TYPEHASH,
            delegatee,
            nonce,
            expiry
        )
    );

    bytes32 digest = keccak256(
        abi.encodePacked(
            "\x19\x01",
            domainSeparator,
            structHash
        )
    );

    address signatory = ecrecover(digest, v, r, s);
    require(signatory != address(0), "BUNNY::delegateBySig: invalid signature");
    require(nonce == nonces[signatory]++, "BUNNY::delegateBySig: invalid nonce");
    require(now <= expiry, "BUNNY::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, "BUNNY::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 = balanceOf(delegator); // balance of underlying BUNNYs (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, "BUNNY::_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;
}

}

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