Contract Source Code:
File 1 of 1 : BaseV1Fees
// SPDX-License-Identifier: MIT
pragma solidity 0.8.11;
interface erc20 {
function totalSupply() external view returns (uint256);
function transfer(address recipient, uint amount) external returns (bool);
function decimals() external view returns (uint8);
function symbol() external view returns (string memory);
function balanceOf(address) external view returns (uint);
function transferFrom(address sender, address recipient, uint amount) external returns (bool);
function approve(address spender, uint value) external returns (bool);
}
library Math {
function min(uint a, uint b) internal pure returns (uint) {
return a < b ? a : b;
}
function sqrt(uint y) internal pure returns (uint z) {
if (y > 3) {
z = y;
uint x = y / 2 + 1;
while (x < z) {
z = x;
x = (y / x + x) / 2;
}
} else if (y != 0) {
z = 1;
}
}
}
interface IBaseV1Callee {
function hook(address sender, uint amount0, uint amount1, bytes calldata data) external;
}
// Base V1 Fees contract is used as a 1:1 pair relationship to split out fees, this ensures that the curve does not need to be modified for LP shares
contract BaseV1Fees {
address internal immutable pair; // The pair it is bonded to
address internal immutable token0; // token0 of pair, saved localy and statically for gas optimization
address internal immutable token1; // Token1 of pair, saved localy and statically for gas optimization
constructor(address _token0, address _token1) {
pair = msg.sender;
token0 = _token0;
token1 = _token1;
}
function _safeTransfer(address token,address to,uint256 value) internal {
require(token.code.length > 0);
(bool success, bytes memory data) =
token.call(abi.encodeWithSelector(erc20.transfer.selector, to, value));
require(success && (data.length == 0 || abi.decode(data, (bool))));
}
// Allow the pair to transfer fees to users
function claimFeesFor(address recipient, uint amount0, uint amount1) external {
require(msg.sender == pair);
if (amount0 > 0) _safeTransfer(token0, recipient, amount0);
if (amount1 > 0) _safeTransfer(token1, recipient, amount1);
}
}
// The base pair of pools, either stable or volatile
contract BaseV1Pair {
string public name;
string public symbol;
uint8 public constant decimals = 18;
// Used to denote stable or volatile pair, not immutable since construction happens in the initialize method for CREATE2 deterministic addresses
bool public immutable stable;
uint public totalSupply = 0;
mapping(address => mapping (address => uint)) public allowance;
mapping(address => uint) public balanceOf;
bytes32 internal DOMAIN_SEPARATOR;
// keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
bytes32 internal constant PERMIT_TYPEHASH = 0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;
mapping(address => uint) public nonces;
uint internal constant MINIMUM_LIQUIDITY = 10**3;
address public immutable token0;
address public immutable token1;
address public immutable fees;
address immutable factory;
// Structure to capture time period obervations every 30 minutes, used for local oracles
struct Observation {
uint timestamp;
uint reserve0Cumulative;
uint reserve1Cumulative;
}
// Capture oracle reading every 30 minutes
uint constant periodSize = 1800;
Observation[] public observations;
uint internal immutable decimals0;
uint internal immutable decimals1;
uint public reserve0;
uint public reserve1;
uint public blockTimestampLast;
uint public reserve0CumulativeLast;
uint public reserve1CumulativeLast;
// index0 and index1 are used to accumulate fees, this is split out from normal trades to keep the swap "clean"
// this further allows LP holders to easily claim fees for tokens they have/staked
uint public index0 = 0;
uint public index1 = 0;
// position assigned to each LP to track their current index0 & index1 vs the global position
mapping(address => uint) public supplyIndex0;
mapping(address => uint) public supplyIndex1;
// tracks the amount of unclaimed, but claimable tokens off of fees for token0 and token1
mapping(address => uint) public claimable0;
mapping(address => uint) public claimable1;
event Fees(address indexed sender, uint amount0, uint amount1);
event Mint(address indexed sender, uint amount0, uint amount1);
event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
event Swap(
address indexed sender,
uint amount0In,
uint amount1In,
uint amount0Out,
uint amount1Out,
address indexed to
);
event Sync(uint reserve0, uint reserve1);
event Claim(address indexed sender, address indexed recipient, uint amount0, uint amount1);
event Transfer(address indexed from, address indexed to, uint amount);
event Approval(address indexed owner, address indexed spender, uint amount);
constructor() {
factory = msg.sender;
(address _token0, address _token1, bool _stable) = BaseV1Factory(msg.sender).getInitializable();
(token0, token1, stable) = (_token0, _token1, _stable);
fees = address(new BaseV1Fees(_token0, _token1));
if (_stable) {
name = string(abi.encodePacked("StableV1 AMM - ", erc20(_token0).symbol(), "/", erc20(_token1).symbol()));
symbol = string(abi.encodePacked("sAMM-", erc20(_token0).symbol(), "/", erc20(_token1).symbol()));
} else {
name = string(abi.encodePacked("VolatileV1 AMM - ", erc20(_token0).symbol(), "/", erc20(_token1).symbol()));
symbol = string(abi.encodePacked("vAMM-", erc20(_token0).symbol(), "/", erc20(_token1).symbol()));
}
decimals0 = 10**erc20(_token0).decimals();
decimals1 = 10**erc20(_token1).decimals();
observations.push(Observation(block.timestamp, 0, 0));
}
// simple re-entrancy check
uint internal _unlocked = 1;
modifier lock() {
require(_unlocked == 1);
_unlocked = 2;
_;
_unlocked = 1;
}
function observationLength() external view returns (uint) {
return observations.length;
}
function lastObservation() public view returns (Observation memory) {
return observations[observations.length-1];
}
function metadata() external view returns (uint dec0, uint dec1, uint r0, uint r1, bool st, address t0, address t1) {
return (decimals0, decimals1, reserve0, reserve1, stable, token0, token1);
}
function tokens() external view returns (address, address) {
return (token0, token1);
}
// claim accumulated but unclaimed fees (viewable via claimable0 and claimable1)
function claimFees() external returns (uint claimed0, uint claimed1) {
_updateFor(msg.sender);
claimed0 = claimable0[msg.sender];
claimed1 = claimable1[msg.sender];
if (claimed0 > 0 || claimed1 > 0) {
claimable0[msg.sender] = 0;
claimable1[msg.sender] = 0;
BaseV1Fees(fees).claimFeesFor(msg.sender, claimed0, claimed1);
emit Claim(msg.sender, msg.sender, claimed0, claimed1);
}
}
// Accrue fees on token0
function _update0(uint amount) internal {
_safeTransfer(token0, fees, amount); // transfer the fees out to BaseV1Fees
uint256 _ratio = amount * 1e18 / totalSupply; // 1e18 adjustment is removed during claim
if (_ratio > 0) {
index0 += _ratio;
}
emit Fees(msg.sender, amount, 0);
}
// Accrue fees on token1
function _update1(uint amount) internal {
_safeTransfer(token1, fees, amount);
uint256 _ratio = amount * 1e18 / totalSupply;
if (_ratio > 0) {
index1 += _ratio;
}
emit Fees(msg.sender, 0, amount);
}
// this function MUST be called on any balance changes, otherwise can be used to infinitely claim fees
// Fees are segregated from core funds, so fees can never put liquidity at risk
function _updateFor(address recipient) internal {
uint _supplied = balanceOf[recipient]; // get LP balance of `recipient`
if (_supplied > 0) {
uint _supplyIndex0 = supplyIndex0[recipient]; // get last adjusted index0 for recipient
uint _supplyIndex1 = supplyIndex1[recipient];
uint _index0 = index0; // get global index0 for accumulated fees
uint _index1 = index1;
supplyIndex0[recipient] = _index0; // update user current position to global position
supplyIndex1[recipient] = _index1;
uint _delta0 = _index0 - _supplyIndex0; // see if there is any difference that need to be accrued
uint _delta1 = _index1 - _supplyIndex1;
if (_delta0 > 0) {
uint _share = _supplied * _delta0 / 1e18; // add accrued difference for each supplied token
claimable0[recipient] += _share;
}
if (_delta1 > 0) {
uint _share = _supplied * _delta1 / 1e18;
claimable1[recipient] += _share;
}
} else {
supplyIndex0[recipient] = index0; // new users are set to the default global state
supplyIndex1[recipient] = index1;
}
}
function getReserves() public view returns (uint _reserve0, uint _reserve1, uint _blockTimestampLast) {
_reserve0 = reserve0;
_reserve1 = reserve1;
_blockTimestampLast = blockTimestampLast;
}
// update reserves and, on the first call per block, price accumulators
function _update(uint balance0, uint balance1, uint _reserve0, uint _reserve1) internal {
uint blockTimestamp = block.timestamp;
uint timeElapsed = blockTimestamp - blockTimestampLast; // overflow is desired
if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {
reserve0CumulativeLast += _reserve0 * timeElapsed;
reserve1CumulativeLast += _reserve1 * timeElapsed;
}
Observation memory _point = lastObservation();
timeElapsed = blockTimestamp - _point.timestamp; // compare the last observation with current timestamp, if greater than 30 minutes, record a new event
if (timeElapsed > periodSize) {
observations.push(Observation(blockTimestamp, reserve0CumulativeLast, reserve1CumulativeLast));
}
reserve0 = balance0;
reserve1 = balance1;
blockTimestampLast = blockTimestamp;
emit Sync(reserve0, reserve1);
}
// produces the cumulative price using counterfactuals to save gas and avoid a call to sync.
function currentCumulativePrices() public view returns (uint reserve0Cumulative, uint reserve1Cumulative, uint blockTimestamp) {
blockTimestamp = block.timestamp;
reserve0Cumulative = reserve0CumulativeLast;
reserve1Cumulative = reserve1CumulativeLast;
// if time has elapsed since the last update on the pair, mock the accumulated price values
(uint _reserve0, uint _reserve1, uint _blockTimestampLast) = getReserves();
if (_blockTimestampLast != blockTimestamp) {
// subtraction overflow is desired
uint timeElapsed = blockTimestamp - _blockTimestampLast;
reserve0Cumulative += _reserve0 * timeElapsed;
reserve1Cumulative += _reserve1 * timeElapsed;
}
}
// gives the current twap price measured from amountIn * tokenIn gives amountOut
function current(address tokenIn, uint amountIn) external view returns (uint amountOut) {
Observation memory _observation = lastObservation();
(uint reserve0Cumulative, uint reserve1Cumulative,) = currentCumulativePrices();
if (block.timestamp == _observation.timestamp) {
_observation = observations[observations.length-2];
}
uint timeElapsed = block.timestamp - _observation.timestamp;
uint _reserve0 = (reserve0Cumulative - _observation.reserve0Cumulative) / timeElapsed;
uint _reserve1 = (reserve1Cumulative - _observation.reserve1Cumulative) / timeElapsed;
amountOut = _getAmountOut(amountIn, tokenIn, _reserve0, _reserve1);
}
// as per `current`, however allows user configured granularity, up to the full window size
function quote(address tokenIn, uint amountIn, uint granularity) external view returns (uint amountOut) {
uint [] memory _prices = sample(tokenIn, amountIn, granularity, 1);
uint priceAverageCumulative;
for (uint i = 0; i < _prices.length; i++) {
priceAverageCumulative += _prices[i];
}
return priceAverageCumulative / granularity;
}
// returns a memory set of twap prices
function prices(address tokenIn, uint amountIn, uint points) external view returns (uint[] memory) {
return sample(tokenIn, amountIn, points, 1);
}
function sample(address tokenIn, uint amountIn, uint points, uint window) public view returns (uint[] memory) {
uint[] memory _prices = new uint[](points);
uint length = observations.length-1;
uint i = length - (points * window);
uint nextIndex = 0;
uint index = 0;
for (; i < length; i+=window) {
nextIndex = i + window;
uint timeElapsed = observations[nextIndex].timestamp - observations[i].timestamp;
uint _reserve0 = (observations[nextIndex].reserve0Cumulative - observations[i].reserve0Cumulative) / timeElapsed;
uint _reserve1 = (observations[nextIndex].reserve1Cumulative - observations[i].reserve1Cumulative) / timeElapsed;
_prices[index] = _getAmountOut(amountIn, tokenIn, _reserve0, _reserve1);
index = index + 1;
}
return _prices;
}
// this low-level function should be called from a contract which performs important safety checks
// standard uniswap v2 implementation
function mint(address to) external lock returns (uint liquidity) {
(uint _reserve0, uint _reserve1) = (reserve0, reserve1);
uint _balance0 = erc20(token0).balanceOf(address(this));
uint _balance1 = erc20(token1).balanceOf(address(this));
uint _amount0 = _balance0 - _reserve0;
uint _amount1 = _balance1 - _reserve1;
uint _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
if (_totalSupply == 0) {
liquidity = Math.sqrt(_amount0 * _amount1) - MINIMUM_LIQUIDITY;
_mint(address(0), MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
} else {
liquidity = Math.min(_amount0 * _totalSupply / _reserve0, _amount1 * _totalSupply / _reserve1);
}
require(liquidity > 0, 'ILM'); // BaseV1: INSUFFICIENT_LIQUIDITY_MINTED
_mint(to, liquidity);
_update(_balance0, _balance1, _reserve0, _reserve1);
emit Mint(msg.sender, _amount0, _amount1);
}
// this low-level function should be called from a contract which performs important safety checks
// standard uniswap v2 implementation
function burn(address to) external lock returns (uint amount0, uint amount1) {
(uint _reserve0, uint _reserve1) = (reserve0, reserve1);
(address _token0, address _token1) = (token0, token1);
uint _balance0 = erc20(_token0).balanceOf(address(this));
uint _balance1 = erc20(_token1).balanceOf(address(this));
uint _liquidity = balanceOf[address(this)];
uint _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
amount0 = _liquidity * _balance0 / _totalSupply; // using balances ensures pro-rata distribution
amount1 = _liquidity * _balance1 / _totalSupply; // using balances ensures pro-rata distribution
require(amount0 > 0 && amount1 > 0, 'ILB'); // BaseV1: INSUFFICIENT_LIQUIDITY_BURNED
_burn(address(this), _liquidity);
_safeTransfer(_token0, to, amount0);
_safeTransfer(_token1, to, amount1);
_balance0 = erc20(_token0).balanceOf(address(this));
_balance1 = erc20(_token1).balanceOf(address(this));
_update(_balance0, _balance1, _reserve0, _reserve1);
emit Burn(msg.sender, amount0, amount1, to);
}
// this low-level function should be called from a contract which performs important safety checks
function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external lock {
require(!BaseV1Factory(factory).isPaused());
require(amount0Out > 0 || amount1Out > 0, 'IOA'); // BaseV1: INSUFFICIENT_OUTPUT_AMOUNT
(uint _reserve0, uint _reserve1) = (reserve0, reserve1);
require(amount0Out < _reserve0 && amount1Out < _reserve1, 'IL'); // BaseV1: INSUFFICIENT_LIQUIDITY
uint _balance0;
uint _balance1;
{ // scope for _token{0,1}, avoids stack too deep errors
(address _token0, address _token1) = (token0, token1);
require(to != _token0 && to != _token1, 'IT'); // BaseV1: INVALID_TO
if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
if (data.length > 0) IBaseV1Callee(to).hook(msg.sender, amount0Out, amount1Out, data); // callback, used for flash loans
_balance0 = erc20(_token0).balanceOf(address(this));
_balance1 = erc20(_token1).balanceOf(address(this));
}
uint amount0In = _balance0 > _reserve0 - amount0Out ? _balance0 - (_reserve0 - amount0Out) : 0;
uint amount1In = _balance1 > _reserve1 - amount1Out ? _balance1 - (_reserve1 - amount1Out) : 0;
require(amount0In > 0 || amount1In > 0, 'IIA'); // BaseV1: INSUFFICIENT_INPUT_AMOUNT
{ // scope for reserve{0,1}Adjusted, avoids stack too deep errors
(address _token0, address _token1) = (token0, token1);
if (amount0In > 0) _update0(amount0In / 10000); // accrue fees for token0 and move them out of pool
if (amount1In > 0) _update1(amount1In / 10000); // accrue fees for token1 and move them out of pool
_balance0 = erc20(_token0).balanceOf(address(this)); // since we removed tokens, we need to reconfirm balances, can also simply use previous balance - amountIn/ 10000, but doing balanceOf again as safety check
_balance1 = erc20(_token1).balanceOf(address(this));
// The curve, either x3y+y3x for stable pools, or x*y for volatile pools
require(_k(_balance0, _balance1) >= _k(_reserve0, _reserve1), 'K'); // BaseV1: K
}
_update(_balance0, _balance1, _reserve0, _reserve1);
emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
}
// force balances to match reserves
function skim(address to) external lock {
(address _token0, address _token1) = (token0, token1);
_safeTransfer(_token0, to, erc20(_token0).balanceOf(address(this)) - (reserve0));
_safeTransfer(_token1, to, erc20(_token1).balanceOf(address(this)) - (reserve1));
}
// force reserves to match balances
function sync() external lock {
_update(erc20(token0).balanceOf(address(this)), erc20(token1).balanceOf(address(this)), reserve0, reserve1);
}
function _f(uint x0, uint y) internal pure returns (uint) {
return x0*(y*y/1e18*y/1e18)/1e18+(x0*x0/1e18*x0/1e18)*y/1e18;
}
function _d(uint x0, uint y) internal pure returns (uint) {
return 3*x0*(y*y/1e18)/1e18+(x0*x0/1e18*x0/1e18);
}
function _get_y(uint x0, uint xy, uint y) internal pure returns (uint) {
for (uint i = 0; i < 255; i++) {
uint y_prev = y;
uint k = _f(x0, y);
if (k < xy) {
uint dy = (xy - k)*1e18/_d(x0, y);
y = y + dy;
} else {
uint dy = (k - xy)*1e18/_d(x0, y);
y = y - dy;
}
if (y > y_prev) {
if (y - y_prev <= 1) {
return y;
}
} else {
if (y_prev - y <= 1) {
return y;
}
}
}
return y;
}
function getAmountOut(uint amountIn, address tokenIn) external view returns (uint) {
(uint _reserve0, uint _reserve1) = (reserve0, reserve1);
amountIn -= amountIn / 10000; // remove fee from amount received
return _getAmountOut(amountIn, tokenIn, _reserve0, _reserve1);
}
function _getAmountOut(uint amountIn, address tokenIn, uint _reserve0, uint _reserve1) internal view returns (uint) {
if (stable) {
uint xy = _k(_reserve0, _reserve1);
_reserve0 = _reserve0 * 1e18 / decimals0;
_reserve1 = _reserve1 * 1e18 / decimals1;
(uint reserveA, uint reserveB) = tokenIn == token0 ? (_reserve0, _reserve1) : (_reserve1, _reserve0);
amountIn = tokenIn == token0 ? amountIn * 1e18 / decimals0 : amountIn * 1e18 / decimals1;
uint y = reserveB - _get_y(amountIn+reserveA, xy, reserveB);
return y * (tokenIn == token0 ? decimals1 : decimals0) / 1e18;
} else {
(uint reserveA, uint reserveB) = tokenIn == token0 ? (_reserve0, _reserve1) : (_reserve1, _reserve0);
return amountIn * reserveB / (reserveA + amountIn);
}
}
function _k(uint x, uint y) internal view returns (uint) {
if (stable) {
uint _x = x * 1e18 / decimals0;
uint _y = y * 1e18 / decimals1;
uint _a = (_x * _y) / 1e18;
uint _b = ((_x * _x) / 1e18 + (_y * _y) / 1e18);
return _a * _b / 1e18; // x3y+y3x >= k
} else {
return x * y; // xy >= k
}
}
function _mint(address dst, uint amount) internal {
_updateFor(dst); // balances must be updated on mint/burn/transfer
totalSupply += amount;
balanceOf[dst] += amount;
emit Transfer(address(0), dst, amount);
}
function _burn(address dst, uint amount) internal {
_updateFor(dst);
totalSupply -= amount;
balanceOf[dst] -= amount;
emit Transfer(dst, address(0), amount);
}
function approve(address spender, uint amount) external returns (bool) {
allowance[msg.sender][spender] = amount;
emit Approval(msg.sender, spender, amount);
return true;
}
function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
require(deadline >= block.timestamp, 'BaseV1: EXPIRED');
DOMAIN_SEPARATOR = keccak256(
abi.encode(
keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'),
keccak256(bytes(name)),
keccak256('1'),
block.chainid,
address(this)
)
);
bytes32 digest = keccak256(
abi.encodePacked(
'\x19\x01',
DOMAIN_SEPARATOR,
keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, nonces[owner]++, deadline))
)
);
address recoveredAddress = ecrecover(digest, v, r, s);
require(recoveredAddress != address(0) && recoveredAddress == owner, 'BaseV1: INVALID_SIGNATURE');
allowance[owner][spender] = value;
emit Approval(owner, spender, value);
}
function transfer(address dst, uint amount) external returns (bool) {
_transferTokens(msg.sender, dst, amount);
return true;
}
function transferFrom(address src, address dst, uint amount) external returns (bool) {
address spender = msg.sender;
uint spenderAllowance = allowance[src][spender];
if (spender != src && spenderAllowance != type(uint).max) {
uint newAllowance = spenderAllowance - amount;
allowance[src][spender] = newAllowance;
emit Approval(src, spender, newAllowance);
}
_transferTokens(src, dst, amount);
return true;
}
function _transferTokens(address src, address dst, uint amount) internal {
_updateFor(src); // update fee position for src
_updateFor(dst); // update fee position for dst
balanceOf[src] -= amount;
balanceOf[dst] += amount;
emit Transfer(src, dst, amount);
}
function _safeTransfer(address token,address to,uint256 value) internal {
require(token.code.length > 0);
(bool success, bytes memory data) =
token.call(abi.encodeWithSelector(erc20.transfer.selector, to, value));
require(success && (data.length == 0 || abi.decode(data, (bool))));
}
}
contract BaseV1Factory {
bool public isPaused;
address public pauser;
address public pendingPauser;
mapping(address => mapping(address => mapping(bool => address))) public getPair;
address[] public allPairs;
mapping(address => bool) public isPair; // simplified check if its a pair, given that `stable` flag might not be available in peripherals
address internal _temp0;
address internal _temp1;
bool internal _temp;
event PairCreated(address indexed token0, address indexed token1, bool stable, address pair, uint);
constructor() {
pauser = msg.sender;
isPaused = false;
}
function allPairsLength() external view returns (uint) {
return allPairs.length;
}
function setPauser(address _pauser) external {
require(msg.sender == pauser);
pendingPauser = _pauser;
}
function acceptPauser() external {
require(msg.sender == pendingPauser);
pauser = pendingPauser;
}
function setPause(bool _state) external {
require(msg.sender == pauser);
isPaused = _state;
}
function pairCodeHash() external pure returns (bytes32) {
return keccak256(type(BaseV1Pair).creationCode);
}
function getInitializable() external view returns (address, address, bool) {
return (_temp0, _temp1, _temp);
}
function createPair(address tokenA, address tokenB, bool stable) external returns (address pair) {
require(tokenA != tokenB, 'IA'); // BaseV1: IDENTICAL_ADDRESSES
(address token0, address token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
require(token0 != address(0), 'ZA'); // BaseV1: ZERO_ADDRESS
require(getPair[token0][token1][stable] == address(0), 'PE'); // BaseV1: PAIR_EXISTS - single check is sufficient
bytes32 salt = keccak256(abi.encodePacked(token0, token1, stable)); // notice salt includes stable as well, 3 parameters
(_temp0, _temp1, _temp) = (token0, token1, stable);
pair = address(new BaseV1Pair{salt:salt}());
getPair[token0][token1][stable] = pair;
getPair[token1][token0][stable] = pair; // populate mapping in the reverse direction
allPairs.push(pair);
isPair[pair] = true;
emit PairCreated(token0, token1, stable, pair, allPairs.length);
}
}