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UNI vs RING

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/**

// SPDX-License-Identifier: GPL-2.0-or-later

*Submitted for verification at Etherscan.io on 2020-09-16

pragma solidity =0.7.6;

/**

*Submitted for verification at Etherscan.io on 2020-09-15

pragma solidity ^0.5.16;

pragma experimental ABIEncoderV2;

// From https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/Math.sol

// Forked from Uniswap's UNI

// Subject to the MIT license.

// Reference: https://etherscan.io/address/0x1f9840a85d5af5bf1d1762f925bdaddc4201f984#code

/**

* @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 addition of two unsigned integers, reverting with custom message on overflow.

* Counterpart to Solidity's `+` operator.

* Requirements:

* - Addition cannot overflow.

function add(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {

uint256 c = a + b;

require(c >= a, errorMessage);

return c;

}

/**

* @dev Returns the subtraction of two unsigned integers, reverting on underflow (when the result is negative).

* Counterpart to Solidity's `-` operator.

* Requirements:

* - Subtraction cannot underflow.

function sub(uint256 a, uint256 b) internal pure returns (uint256) {

return sub(a, b, "SafeMath: subtraction underflow");

}

/**

* @dev Returns the subtraction of two unsigned integers, reverting with custom message on underflow (when the result is negative).

* Counterpart to Solidity's `-` operator.

* Requirements:

* - Subtraction cannot underflow.

function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {

require(b <= a, errorMessage);

uint256 c = a - b;

return c;

}

/**

* @dev Returns the multiplication of two unsigned integers, reverting on overflow.

* Counterpart to Solidity's `*` operator.

* Requirements:

* - Multiplication cannot overflow.

function mul(uint256 a, uint256 b) internal pure returns (uint256) {

// Gas optimization: this is cheaper than requiring 'a' not being zero, but the

// benefit is lost if 'b' is also tested.

// See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522

if (a == 0) {

return 0;

}

uint256 c = a * b;

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

return c;

}

/**

* @dev Returns the multiplication of two unsigned integers, reverting on overflow.

* Counterpart to Solidity's `*` operator.

* Requirements:

* - Multiplication cannot overflow.

function mul(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {

// Gas optimization: this is cheaper than requiring 'a' not being zero, but the

// benefit is lost if 'b' is also tested.

// See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522

if (a == 0) {

return 0;

}

uint256 c = a * b;

require(c / a == b, errorMessage);

return c;

}

/**

contract Ring {

* @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) {

// Solidity only automatically asserts when dividing by 0

require(b > 0, errorMessage);

uint256 c = a / b;

// assert(a == b * c + a % b); // There is no case in which this doesn't hold

return c;

}

/**

* @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),

* Reverts when dividing by zero.

* Counterpart to Solidity's `%` operator. This function uses a `revert`

* opcode (which leaves remaining gas untouched) while Solidity uses an

* invalid opcode to revert (consuming all remaining gas).

* Requirements:

* - The divisor cannot be zero.

function mod(uint256 a, uint256 b) internal pure returns (uint256) {

return mod(a, b, "SafeMath: modulo by zero");

}

/**

* @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),

* Reverts with custom message when dividing by zero.

* Counterpart to Solidity's `%` operator. This function uses a `revert`

* opcode (which leaves remaining gas untouched) while Solidity uses an

* invalid opcode to revert (consuming all remaining gas).

* Requirements:

* - The divisor cannot be zero.

function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {

require(b != 0, errorMessage);

return a % b;

}

contract Uni {

/// @notice EIP-20 token name for this token

string public constant name = "Uniswap";

// solhint-disable-next-line const-name-snakecase

string public constant name = "Ring";

/// @notice EIP-20 token symbol for this token

string public constant symbol = "UNI";

// solhint-disable-next-line const-name-snakecase

string public constant symbol = "RING";

/// @notice EIP-20 token decimals for this token

// solhint-disable-next-line const-name-snakecase

uint8 public constant decimals = 18;

/// @notice Total number of tokens in circulation

uint public totalSupply = 1_000_000_000e18; // 1 billion Uni

// solhint-disable-next-line const-name-snakecase

uint public totalSupply = 1_000_000_000e18; // 1 billion Ring

/// @notice Address which may mint new tokens

address public minter;

/// @notice The timestamp after which minting may occur

uint public mintingAllowedAfter;

/// @notice Minimum time between mints

uint32 public constant minimumTimeBetweenMints = 1 days * 365;

/// @notice Cap on the percentage of totalSupply that can be minted at each mint

uint8 public constant mintCap = 2;

/// @notice Allowance amounts on behalf of others

mapping (address => mapping (address => uint96)) internal allowances;

/// @notice Official record of token balances for each account

mapping (address => uint96) internal balances;

/// @notice A record of each accounts delegate

mapping (address => address) public delegates;

/// @notice A checkpoint for marking number of votes from a given block

struct Checkpoint {

uint32 fromBlock;

uint96 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 The EIP-712 typehash for the permit struct used by the contract

bytes32 public constant PERMIT_TYPEHASH = keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");

/// @notice A record of states for signing / validating signatures

mapping (address => uint) public nonces;

/// @notice An event thats emitted when the minter address is changed

event MinterChanged(address minter, address newMinter);

/// @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 The standard EIP-20 transfer event

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

/// @notice The standard EIP-20 approval event

event Approval(address indexed owner, address indexed spender, uint256 amount);

/**

* @notice Construct a new Uni token

* @notice Construct a new Ring token

* @param account The initial account to grant all the tokens

* @param minter_ The account with minting ability

* @param mintingAllowedAfter_ The timestamp after which minting may occur

constructor(address account, address minter_, uint mintingAllowedAfter_) public {

constructor(address account, address minter_) {

require(mintingAllowedAfter_ >= block.timestamp, "Uni::constructor: minting can only begin after deployment");

balances[account] = uint96(totalSupply);

emit Transfer(address(0), account, totalSupply);

minter = minter_;

emit MinterChanged(address(0), minter);

mintingAllowedAfter = mintingAllowedAfter_;

}

/**

* @notice Change the minter address

* @param minter_ The address of the new minter

function setMinter(address minter_) external {

require(msg.sender == minter, "Uni::setMinter: only the minter can change the minter address");

require(msg.sender == minter, "Ring: only the minter can change the minter address");

emit MinterChanged(minter, minter_);

minter = minter_;

}

/**

* @notice Mint new tokens

* @param dst The address of the destination account

* @param rawAmount The number of tokens to be minted

function mint(address dst, uint rawAmount) external {

require(msg.sender == minter, "Uni::mint: only the minter can mint");

require(msg.sender == minter, "Ring: only the minter can mint");

require(block.timestamp >= mintingAllowedAfter, "Uni::mint: minting not allowed yet");

require(dst != address(0), "Ring: cannot transfer to the zero address");

require(dst != address(0), "Uni::mint: cannot transfer to the zero address");

// record the mint

mintingAllowedAfter = SafeMath.add(block.timestamp, minimumTimeBetweenMints);

// mint the amount

uint96 amount = safe96(rawAmount, "Uni::mint: amount exceeds 96 bits");

uint96 amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");

require(amount <= SafeMath.div(SafeMath.mul(totalSupply, mintCap), 100), "Uni::mint: exceeded mint cap");

uint96 safeSupply = safe96(totalSupply, "Ring: totalSupply exceeds 96 bits");

totalSupply = safe96(SafeMath.add(totalSupply, amount), "Uni::mint: totalSupply exceeds 96 bits");

totalSupply = add96(safeSupply, amount, "Ring: totalSupply exceeds 96 bits");

// transfer the amount to the recipient

balances[dst] = add96(balances[dst], amount, "Uni::mint: transfer amount overflows");

balances[dst] = add96(balances[dst], amount, "Ring: transfer amount overflows");

emit Transfer(address(0), dst, amount);

// move delegates

_moveDelegates(address(0), delegates[dst], amount);

}

/**

* @notice Get the number of tokens `spender` is approved to spend on behalf of `account`

* @param account The address of the account holding the funds

* @param spender The address of the account spending the funds

* @return The number of tokens approved

function allowance(address account, address spender) external view returns (uint) {

return allowances[account][spender];

}

/**

* @notice Approve `spender` to transfer up to `amount` from `src`

* @dev This will overwrite the approval amount for `spender`

* and is subject to issues noted [here](https://eips.ethereum.org/EIPS/eip-20#approve)

* @param spender The address of the account which may transfer tokens

* @param rawAmount The number of tokens that are approved (2^256-1 means infinite)

* @return Whether or not the approval succeeded

function approve(address spender, uint rawAmount) external returns (bool) {

uint96 amount;

if (rawAmount == uint(-1)) {

amount = uint96(-1);

} else {

amount = safe96(rawAmount, "Uni::approve: amount exceeds 96 bits");

amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");

}

allowances[msg.sender][spender] = amount;

emit Approval(msg.sender, spender, amount);

return true;

}

/**

* @notice Triggers an approval from owner to spends

* @param owner The address to approve from

* @param spender The address to be approved

* @param rawAmount The number of tokens that are approved (2^256-1 means infinite)

* @param deadline 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 permit(address owner, address spender, uint rawAmount, uint deadline, uint8 v, bytes32 r, bytes32 s) external {

uint96 amount;

if (rawAmount == uint(-1)) {

amount = uint96(-1);

} else {

amount = safe96(rawAmount, "Uni::permit: amount exceeds 96 bits");

amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");

}

bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), getChainId(), address(this)));

bytes32 structHash = keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, rawAmount, nonces[owner]++, deadline));

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

address signatory = ecrecover(digest, v, r, s);

require(signatory != address(0), "Uni::permit: invalid signature");

require(signatory != address(0), "Ring: invalid signature");

require(signatory == owner, "Uni::permit: unauthorized");

require(signatory == owner, "Ring: unauthorized");

require(now <= deadline, "Uni::permit: signature expired");

// solhint-disable-next-line not-rely-on-time

require(block.timestamp <= deadline, "Ring: signature expired");

allowances[owner][spender] = amount;

emit Approval(owner, spender, amount);

}

/**

* @notice Get the number of tokens held by the `account`

* @param account The address of the account to get the balance of

* @return The number of tokens held

function balanceOf(address account) external view returns (uint) {

return balances[account];

}

/**

* @notice Transfer `amount` tokens from `msg.sender` to `dst`

* @param dst The address of the destination account

* @param rawAmount The number of tokens to transfer

* @return Whether or not the transfer succeeded

function transfer(address dst, uint rawAmount) external returns (bool) {

uint96 amount = safe96(rawAmount, "Uni::transfer: amount exceeds 96 bits");

uint96 amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");

_transferTokens(msg.sender, dst, amount);

return true;

}

/**

* @notice Transfer `amount` tokens from `src` to `dst`

* @param src The address of the source account

* @param dst The address of the destination account

* @param rawAmount The number of tokens to transfer

* @return Whether or not the transfer succeeded

function transferFrom(address src, address dst, uint rawAmount) external returns (bool) {

address spender = msg.sender;

uint96 spenderAllowance = allowances[src][spender];

uint96 amount = safe96(rawAmount, "Uni::approve: amount exceeds 96 bits");

uint96 amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");

if (spender != src && spenderAllowance != uint96(-1)) {

uint96 newAllowance = sub96(spenderAllowance, amount, "Uni::transferFrom: transfer amount exceeds spender allowance");

uint96 newAllowance = sub96(spenderAllowance, amount, "Ring: transfer amount exceeds spender allowance");

allowances[src][spender] = newAllowance;

emit Approval(src, spender, newAllowance);

}

_transferTokens(src, dst, amount);

return true;

}

/**

* @notice Delegate votes from `msg.sender` to `delegatee`

* @param delegatee The address to delegate votes to

function delegate(address delegatee) public {

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) public {

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), "Uni::delegateBySig: invalid signature");

require(signatory != address(0), "Ring: invalid signature");

require(nonce == nonces[signatory]++, "Uni::delegateBySig: invalid nonce");

require(nonce == nonces[signatory]++, "Ring: invalid nonce");

require(now <= expiry, "Uni::delegateBySig: signature expired");

// solhint-disable-next-line not-rely-on-time

require(block.timestamp <= expiry, "Ring: 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 (uint96) {

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) public view returns (uint96) {

require(blockNumber < block.number, "Uni::getPriorVotes: not yet determined");

require(blockNumber < block.number, "Ring: 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];

uint96 delegatorBalance = balances[delegator];

delegates[delegator] = delegatee;

emit DelegateChanged(delegator, currentDelegate, delegatee);

_moveDelegates(currentDelegate, delegatee, delegatorBalance);

}

function _transferTokens(address src, address dst, uint96 amount) internal {

require(src != address(0), "Uni::_transferTokens: cannot transfer from the zero address");

require(src != address(0), "Ring: cannot transfer from the zero address");

require(dst != address(0), "Uni::_transferTokens: cannot transfer to the zero address");

require(dst != address(0), "Ring: cannot transfer to the zero address");

balances[src] = sub96(balances[src], amount, "Uni::_transferTokens: transfer amount exceeds balance");

balances[src] = sub96(balances[src], amount, "Ring: transfer amount exceeds balance");

balances[dst] = add96(balances[dst], amount, "Uni::_transferTokens: transfer amount overflows");

balances[dst] = add96(balances[dst], amount, "Ring: transfer amount overflows");

emit Transfer(src, dst, amount);

_moveDelegates(delegates[src], delegates[dst], amount);

}

function _moveDelegates(address srcRep, address dstRep, uint96 amount) internal {

if (srcRep != dstRep && amount > 0) {

if (srcRep != address(0)) {

uint32 srcRepNum = numCheckpoints[srcRep];

uint96 srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;

uint96 srcRepNew = sub96(srcRepOld, amount, "Uni::_moveVotes: vote amount underflows");

uint96 srcRepNew = sub96(srcRepOld, amount, "Ring: vote amount underflows");

_writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);

}

if (dstRep != address(0)) {

uint32 dstRepNum = numCheckpoints[dstRep];

uint96 dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;

uint96 dstRepNew = add96(dstRepOld, amount, "Uni::_moveVotes: vote amount overflows");

uint96 dstRepNew = add96(dstRepOld, amount, "Ring: vote amount overflows");

_writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);

}

function _writeCheckpoint(address delegatee, uint32 nCheckpoints, uint96 oldVotes, uint96 newVotes) internal {

uint32 blockNumber = safe32(block.number, "Uni::_writeCheckpoint: block number exceeds 32 bits");

uint32 blockNumber = safe32(block.number, "Ring: 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 safe96(uint n, string memory errorMessage) internal pure returns (uint96) {

require(n < 2**96, errorMessage);

return uint96(n);

}

function add96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {

uint96 c = a + b;

require(c >= a, errorMessage);

return c;

}

function sub96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {

require(b <= a, errorMessage);

return a - b;

}

function getChainId() internal pure returns (uint) {

uint256 chainId;

// solhint-disable-next-line no-inline-assembly

assembly { chainId := chainid() }

return chainId;

}

Saved diffs

Original text

Open file

/**
 *Submitted for verification at Etherscan.io on 2020-09-16
*/

/**
 *Submitted for verification at Etherscan.io on 2020-09-15
*/

pragma solidity ^0.5.16;
pragma experimental ABIEncoderV2;

// From https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/Math.sol
// Subject to the MIT license.

/**
 * @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 addition of two unsigned integers, reverting with custom message on overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, errorMessage);

        return c;
    }

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

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

        return c;
    }

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

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

        return c;
    }

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

        uint256 c = a * b;
        require(c / a == b, errorMessage);

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

        return c;
    }

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

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

contract Uni {
    /// @notice EIP-20 token name for this token
    string public constant name = "Uniswap";

    /// @notice EIP-20 token symbol for this token
    string public constant symbol = "UNI";

    /// @notice EIP-20 token decimals for this token
    uint8 public constant decimals = 18;

    /// @notice Total number of tokens in circulation
    uint public totalSupply = 1_000_000_000e18; // 1 billion Uni

    /// @notice Address which may mint new tokens
    address public minter;

    /// @notice The timestamp after which minting may occur
    uint public mintingAllowedAfter;

    /// @notice Minimum time between mints
    uint32 public constant minimumTimeBetweenMints = 1 days * 365;

    /// @notice Cap on the percentage of totalSupply that can be minted at each mint
    uint8 public constant mintCap = 2;

    /// @notice Allowance amounts on behalf of others
    mapping (address => mapping (address => uint96)) internal allowances;

    /// @notice Official record of token balances for each account
    mapping (address => uint96) internal balances;

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

    /// @notice A checkpoint for marking number of votes from a given block
    struct Checkpoint {
        uint32 fromBlock;
        uint96 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 The EIP-712 typehash for the permit struct used by the contract
    bytes32 public constant PERMIT_TYPEHASH = keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");

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

    /// @notice An event thats emitted when the minter address is changed
    event MinterChanged(address minter, address newMinter);

    /// @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 The standard EIP-20 transfer event
    event Transfer(address indexed from, address indexed to, uint256 amount);

    /// @notice The standard EIP-20 approval event
    event Approval(address indexed owner, address indexed spender, uint256 amount);

    /**
     * @notice Construct a new Uni token
     * @param account The initial account to grant all the tokens
     * @param minter_ The account with minting ability
     * @param mintingAllowedAfter_ The timestamp after which minting may occur
     */
    constructor(address account, address minter_, uint mintingAllowedAfter_) public {
        require(mintingAllowedAfter_ >= block.timestamp, "Uni::constructor: minting can only begin after deployment");

        balances[account] = uint96(totalSupply);
        emit Transfer(address(0), account, totalSupply);
        minter = minter_;
        emit MinterChanged(address(0), minter);
        mintingAllowedAfter = mintingAllowedAfter_;
    }

    /**
     * @notice Change the minter address
     * @param minter_ The address of the new minter
     */
    function setMinter(address minter_) external {
        require(msg.sender == minter, "Uni::setMinter: only the minter can change the minter address");
        emit MinterChanged(minter, minter_);
        minter = minter_;
    }

    /**
     * @notice Mint new tokens
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to be minted
     */
    function mint(address dst, uint rawAmount) external {
        require(msg.sender == minter, "Uni::mint: only the minter can mint");
        require(block.timestamp >= mintingAllowedAfter, "Uni::mint: minting not allowed yet");
        require(dst != address(0), "Uni::mint: cannot transfer to the zero address");

        // record the mint
        mintingAllowedAfter = SafeMath.add(block.timestamp, minimumTimeBetweenMints);

        // mint the amount
        uint96 amount = safe96(rawAmount, "Uni::mint: amount exceeds 96 bits");
        require(amount <= SafeMath.div(SafeMath.mul(totalSupply, mintCap), 100), "Uni::mint: exceeded mint cap");
        totalSupply = safe96(SafeMath.add(totalSupply, amount), "Uni::mint: totalSupply exceeds 96 bits");

        // transfer the amount to the recipient
        balances[dst] = add96(balances[dst], amount, "Uni::mint: transfer amount overflows");
        emit Transfer(address(0), dst, amount);

        // move delegates
        _moveDelegates(address(0), delegates[dst], amount);
    }

    /**
     * @notice Get the number of tokens `spender` is approved to spend on behalf of `account`
     * @param account The address of the account holding the funds
     * @param spender The address of the account spending the funds
     * @return The number of tokens approved
     */
    function allowance(address account, address spender) external view returns (uint) {
        return allowances[account][spender];
    }

    /**
     * @notice Approve `spender` to transfer up to `amount` from `src`
     * @dev This will overwrite the approval amount for `spender`
     *  and is subject to issues noted [here](https://eips.ethereum.org/EIPS/eip-20#approve)
     * @param spender The address of the account which may transfer tokens
     * @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
     * @return Whether or not the approval succeeded
     */
    function approve(address spender, uint rawAmount) external returns (bool) {
        uint96 amount;
        if (rawAmount == uint(-1)) {
            amount = uint96(-1);
        } else {
            amount = safe96(rawAmount, "Uni::approve: amount exceeds 96 bits");
        }

        allowances[msg.sender][spender] = amount;

        emit Approval(msg.sender, spender, amount);
        return true;
    }

    /**
     * @notice Triggers an approval from owner to spends
     * @param owner The address to approve from
     * @param spender The address to be approved
     * @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
     * @param deadline 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 permit(address owner, address spender, uint rawAmount, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
        uint96 amount;
        if (rawAmount == uint(-1)) {
            amount = uint96(-1);
        } else {
            amount = safe96(rawAmount, "Uni::permit: amount exceeds 96 bits");
        }

        bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), getChainId(), address(this)));
        bytes32 structHash = keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, rawAmount, nonces[owner]++, deadline));
        bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
        address signatory = ecrecover(digest, v, r, s);
        require(signatory != address(0), "Uni::permit: invalid signature");
        require(signatory == owner, "Uni::permit: unauthorized");
        require(now <= deadline, "Uni::permit: signature expired");

        allowances[owner][spender] = amount;

        emit Approval(owner, spender, amount);
    }

    /**
     * @notice Get the number of tokens held by the `account`
     * @param account The address of the account to get the balance of
     * @return The number of tokens held
     */
    function balanceOf(address account) external view returns (uint) {
        return balances[account];
    }

    /**
     * @notice Transfer `amount` tokens from `msg.sender` to `dst`
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to transfer
     * @return Whether or not the transfer succeeded
     */
    function transfer(address dst, uint rawAmount) external returns (bool) {
        uint96 amount = safe96(rawAmount, "Uni::transfer: amount exceeds 96 bits");
        _transferTokens(msg.sender, dst, amount);
        return true;
    }

    /**
     * @notice Transfer `amount` tokens from `src` to `dst`
     * @param src The address of the source account
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to transfer
     * @return Whether or not the transfer succeeded
     */
    function transferFrom(address src, address dst, uint rawAmount) external returns (bool) {
        address spender = msg.sender;
        uint96 spenderAllowance = allowances[src][spender];
        uint96 amount = safe96(rawAmount, "Uni::approve: amount exceeds 96 bits");

        if (spender != src && spenderAllowance != uint96(-1)) {
            uint96 newAllowance = sub96(spenderAllowance, amount, "Uni::transferFrom: transfer amount exceeds spender allowance");
            allowances[src][spender] = newAllowance;

            emit Approval(src, spender, newAllowance);
        }

        _transferTokens(src, dst, amount);
        return true;
    }

    /**
     * @notice Delegate votes from `msg.sender` to `delegatee`
     * @param delegatee The address to delegate votes to
     */
    function delegate(address delegatee) public {
        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) public {
        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), "Uni::delegateBySig: invalid signature");
        require(nonce == nonces[signatory]++, "Uni::delegateBySig: invalid nonce");
        require(now <= expiry, "Uni::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 (uint96) {
        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) public view returns (uint96) {
        require(blockNumber < block.number, "Uni::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];
        uint96 delegatorBalance = balances[delegator];
        delegates[delegator] = delegatee;

        emit DelegateChanged(delegator, currentDelegate, delegatee);

        _moveDelegates(currentDelegate, delegatee, delegatorBalance);
    }

    function _transferTokens(address src, address dst, uint96 amount) internal {
        require(src != address(0), "Uni::_transferTokens: cannot transfer from the zero address");
        require(dst != address(0), "Uni::_transferTokens: cannot transfer to the zero address");

        balances[src] = sub96(balances[src], amount, "Uni::_transferTokens: transfer amount exceeds balance");
        balances[dst] = add96(balances[dst], amount, "Uni::_transferTokens: transfer amount overflows");
        emit Transfer(src, dst, amount);

        _moveDelegates(delegates[src], delegates[dst], amount);
    }

    function _moveDelegates(address srcRep, address dstRep, uint96 amount) internal {
        if (srcRep != dstRep && amount > 0) {
            if (srcRep != address(0)) {
                uint32 srcRepNum = numCheckpoints[srcRep];
                uint96 srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;
                uint96 srcRepNew = sub96(srcRepOld, amount, "Uni::_moveVotes: vote amount underflows");
                _writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
            }

            if (dstRep != address(0)) {
                uint32 dstRepNum = numCheckpoints[dstRep];
                uint96 dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;
                uint96 dstRepNew = add96(dstRepOld, amount, "Uni::_moveVotes: vote amount overflows");
                _writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
            }
        }
    }

    function _writeCheckpoint(address delegatee, uint32 nCheckpoints, uint96 oldVotes, uint96 newVotes) internal {
      uint32 blockNumber = safe32(block.number, "Uni::_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 safe96(uint n, string memory errorMessage) internal pure returns (uint96) {
        require(n < 2**96, errorMessage);
        return uint96(n);
    }

    function add96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
        uint96 c = a + b;
        require(c >= a, errorMessage);
        return c;
    }

    function sub96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
        require(b <= a, errorMessage);
        return a - b;
    }

    function getChainId() internal pure returns (uint) {
        uint256 chainId;
        assembly { chainId := chainid() }
        return chainId;
    }
}

Changed text

Open file

// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity =0.7.6;
pragma experimental ABIEncoderV2;

// Forked from Uniswap's UNI
// Reference: https://etherscan.io/address/0x1f9840a85d5af5bf1d1762f925bdaddc4201f984#code

contract Ring {
    /// @notice EIP-20 token name for this token
    // solhint-disable-next-line const-name-snakecase
    string public constant name = "Ring";

    /// @notice EIP-20 token symbol for this token
    // solhint-disable-next-line const-name-snakecase
    string public constant symbol = "RING";

    /// @notice EIP-20 token decimals for this token
    // solhint-disable-next-line const-name-snakecase
    uint8 public constant decimals = 18;

    /// @notice Total number of tokens in circulation
    // solhint-disable-next-line const-name-snakecase
    uint public totalSupply = 1_000_000_000e18; // 1 billion Ring

    /// @notice Address which may mint new tokens
    address public minter;

    mapping (address => mapping (address => uint96)) internal allowances;

    mapping (address => uint96) internal balances;

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

    /// @notice A checkpoint for marking number of votes from a given block
    struct Checkpoint {
        uint32 fromBlock;
        uint96 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 The EIP-712 typehash for the permit struct used by the contract
    bytes32 public constant PERMIT_TYPEHASH = keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");

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

    /// @notice An event thats emitted when the minter address is changed
    event MinterChanged(address minter, address newMinter);

    /// @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 The standard EIP-20 transfer event
    event Transfer(address indexed from, address indexed to, uint256 amount);

    /// @notice The standard EIP-20 approval event
    event Approval(address indexed owner, address indexed spender, uint256 amount);

    /**
     * @notice Construct a new Ring token
     * @param account The initial account to grant all the tokens
     * @param minter_ The account with minting ability
     */
    constructor(address account, address minter_) {
        balances[account] = uint96(totalSupply);
        emit Transfer(address(0), account, totalSupply);
        minter = minter_;
        emit MinterChanged(address(0), minter);
    }

    /**
     * @notice Change the minter address
     * @param minter_ The address of the new minter
     */
    function setMinter(address minter_) external {
        require(msg.sender == minter, "Ring: only the minter can change the minter address");
        emit MinterChanged(minter, minter_);
        minter = minter_;
    }

    /**
     * @notice Mint new tokens
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to be minted
     */
    function mint(address dst, uint rawAmount) external {
        require(msg.sender == minter, "Ring: only the minter can mint");
        require(dst != address(0), "Ring: cannot transfer to the zero address");

        // mint the amount
        uint96 amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");
        uint96 safeSupply = safe96(totalSupply, "Ring: totalSupply exceeds 96 bits");
        totalSupply = add96(safeSupply, amount, "Ring: totalSupply exceeds 96 bits");

        // transfer the amount to the recipient
        balances[dst] = add96(balances[dst], amount, "Ring: transfer amount overflows");
        emit Transfer(address(0), dst, amount);

        // move delegates
        _moveDelegates(address(0), delegates[dst], amount);
    }

    /**
     * @notice Get the number of tokens `spender` is approved to spend on behalf of `account`
     * @param account The address of the account holding the funds
     * @param spender The address of the account spending the funds
     * @return The number of tokens approved
     */
    function allowance(address account, address spender) external view returns (uint) {
        return allowances[account][spender];
    }

    /**
     * @notice Approve `spender` to transfer up to `amount` from `src`
     * @dev This will overwrite the approval amount for `spender`
     *  and is subject to issues noted [here](https://eips.ethereum.org/EIPS/eip-20#approve)
     * @param spender The address of the account which may transfer tokens
     * @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
     * @return Whether or not the approval succeeded
     */
    function approve(address spender, uint rawAmount) external returns (bool) {
        uint96 amount;
        if (rawAmount == uint(-1)) {
            amount = uint96(-1);
        } else {
            amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");
        }

        allowances[msg.sender][spender] = amount;

        emit Approval(msg.sender, spender, amount);
        return true;
    }

    /**
     * @notice Triggers an approval from owner to spends
     * @param owner The address to approve from
     * @param spender The address to be approved
     * @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
     * @param deadline 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 permit(address owner, address spender, uint rawAmount, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
        uint96 amount;
        if (rawAmount == uint(-1)) {
            amount = uint96(-1);
        } else {
            amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");
        }

        bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), getChainId(), address(this)));
        bytes32 structHash = keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, rawAmount, nonces[owner]++, deadline));
        bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
        address signatory = ecrecover(digest, v, r, s);
        require(signatory != address(0), "Ring: invalid signature");
        require(signatory == owner, "Ring: unauthorized");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp <= deadline, "Ring: signature expired");

        allowances[owner][spender] = amount;

        emit Approval(owner, spender, amount);
    }

    /**
     * @notice Get the number of tokens held by the `account`
     * @param account The address of the account to get the balance of
     * @return The number of tokens held
     */
    function balanceOf(address account) external view returns (uint) {
        return balances[account];
    }

    /**
     * @notice Transfer `amount` tokens from `msg.sender` to `dst`
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to transfer
     * @return Whether or not the transfer succeeded
     */
    function transfer(address dst, uint rawAmount) external returns (bool) {
        uint96 amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");
        _transferTokens(msg.sender, dst, amount);
        return true;
    }

    /**
     * @notice Transfer `amount` tokens from `src` to `dst`
     * @param src The address of the source account
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to transfer
     * @return Whether or not the transfer succeeded
     */
    function transferFrom(address src, address dst, uint rawAmount) external returns (bool) {
        address spender = msg.sender;
        uint96 spenderAllowance = allowances[src][spender];
        uint96 amount = safe96(rawAmount, "Ring: amount exceeds 96 bits");

        if (spender != src && spenderAllowance != uint96(-1)) {
            uint96 newAllowance = sub96(spenderAllowance, amount, "Ring: transfer amount exceeds spender allowance");
            allowances[src][spender] = newAllowance;

            emit Approval(src, spender, newAllowance);
        }

        _transferTokens(src, dst, amount);
        return true;
    }

    /**
     * @notice Delegate votes from `msg.sender` to `delegatee`
     * @param delegatee The address to delegate votes to
     */
    function delegate(address delegatee) public {
        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) public {
        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), "Ring: invalid signature");
        require(nonce == nonces[signatory]++, "Ring: invalid nonce");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp <= expiry, "Ring: 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 (uint96) {
        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) public view returns (uint96) {
        require(blockNumber < block.number, "Ring: 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];
        uint96 delegatorBalance = balances[delegator];
        delegates[delegator] = delegatee;

        emit DelegateChanged(delegator, currentDelegate, delegatee);

        _moveDelegates(currentDelegate, delegatee, delegatorBalance);
    }

    function _transferTokens(address src, address dst, uint96 amount) internal {
        require(src != address(0), "Ring: cannot transfer from the zero address");
        require(dst != address(0), "Ring: cannot transfer to the zero address");

        balances[src] = sub96(balances[src], amount, "Ring: transfer amount exceeds balance");
        balances[dst] = add96(balances[dst], amount, "Ring: transfer amount overflows");
        emit Transfer(src, dst, amount);

        _moveDelegates(delegates[src], delegates[dst], amount);
    }

    function _moveDelegates(address srcRep, address dstRep, uint96 amount) internal {
        if (srcRep != dstRep && amount > 0) {
            if (srcRep != address(0)) {
                uint32 srcRepNum = numCheckpoints[srcRep];
                uint96 srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;
                uint96 srcRepNew = sub96(srcRepOld, amount, "Ring: vote amount underflows");
                _writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
            }

            if (dstRep != address(0)) {
                uint32 dstRepNum = numCheckpoints[dstRep];
                uint96 dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;
                uint96 dstRepNew = add96(dstRepOld, amount, "Ring: vote amount overflows");
                _writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
            }
        }
    }

    function _writeCheckpoint(address delegatee, uint32 nCheckpoints, uint96 oldVotes, uint96 newVotes) internal {
      uint32 blockNumber = safe32(block.number, "Ring: 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 safe96(uint n, string memory errorMessage) internal pure returns (uint96) {
        require(n < 2**96, errorMessage);
        return uint96(n);
    }

    function add96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
        uint96 c = a + b;
        require(c >= a, errorMessage);
        return c;
    }

    function sub96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
        require(b <= a, errorMessage);
        return a - b;
    }

    function getChainId() internal pure returns (uint) {
        uint256 chainId;
        // solhint-disable-next-line no-inline-assembly
        assembly { chainId := chainid() }
        return chainId;
    }
}