Contract Source Code:

// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

import { IDeFiveToken } from "./interfaces/IDeFiveToken.sol";

contract DeFiveLP is IDeFiveToken {
    string public constant override name = "DeFive LP Token";
    string public constant override symbol = "DEFIVE-LP";
    uint8 public constant override decimals = 18;
    uint256 public override totalSupply;

    mapping(address => uint256) public override balanceOf;
    mapping(address => mapping(address => uint256)) public override allowance;

    bytes32 public override DOMAIN_SEPARATOR;
    bytes32 public constant override PERMIT_TYPEHASH =
        0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;

    mapping(address => uint256) public override nonces;

    constructor() {
        DOMAIN_SEPARATOR = keccak256(
            abi.encode(
                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
                keccak256(bytes(name)),
                keccak256(bytes("1")),
                block.chainid,
                address(this)
            )
        );
    }

    function _mint(address to, uint256 value) internal {
        totalSupply += value;
        balanceOf[to] += value;
        emit Transfer(address(0), to, value);
    }

    function _burn(address from, uint256 value) internal {
        balanceOf[from] -= value;
        totalSupply -= value;
        emit Transfer(from, address(0), value);
    }

    function _approve(address owner, address spender, uint256 value) private {
        allowance[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    function _transfer(address from, address to, uint256 value) private {
        balanceOf[from] -= value;
        balanceOf[to] += value;
        emit Transfer(from, to, value);
    }

    function approve(address spender, uint256 value) external override returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }

    function transfer(address to, uint256 value) external override returns (bool) {
        _transfer(msg.sender, to, value);
        return true;
    }

    function transferFrom(address from, address to, uint256 value) external override returns (bool) {
        if (allowance[from][msg.sender] != type(uint256).max) {
            allowance[from][msg.sender] -= value;
        }
        _transfer(from, to, value);
        return true;
    }

    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external override {
        require(deadline >= block.timestamp, "DeFive: EXPIRED");
        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, "DeFive: INVALID_SIGNATURE");
        _approve(owner, spender, value);
    }
}

// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

import { IDeFivePair } from "./interfaces/IDeFivePair.sol";
import { DeFiveLP } from "./DeFiveLP.sol";
import { Math } from "./libraries/Math.sol";
import { UQ112x112 } from "./libraries/UQ112x112.sol";
import { IDeFiveToken } from "./interfaces/IDeFiveToken.sol";
import { IDeFiveFactory } from "./interfaces/IDeFiveFactory.sol";
import { IDeFiveCallee } from "./interfaces/IDeFiveCallee.sol";

contract DeFivePair is IDeFivePair, DeFiveLP {
    using UQ112x112 for uint224;

    uint256 public constant override MINIMUM_LIQUIDITY = 10 ** 3;

    address public override factory;
    address public override token0;
    address public override token1;

    uint112 private reserve0;
    uint112 private reserve1;
    uint32 private blockTimestampLast;

    uint256 public override price0CumulativeLast;
    uint256 public override price1CumulativeLast;
    uint256 public override kLast; // reserve0 * reserve1, as of immediately after the most recent liquidity event

    uint256 private unlocked = 1;
    modifier lock() {
        require(unlocked == 1, "DeFive: LOCKED");
        unlocked = 0;
        _;
        unlocked = 1;
    }

    constructor() {
        factory = msg.sender;
    }

    function initialize(address _token0, address _token1) external override {
        require(msg.sender == factory, "DeFive: FORBIDDEN");
        token0 = _token0;
        token1 = _token1;
    }

    function getReserves()
        public
        view
        override
        returns (uint112 _reserve0, uint112 _reserve1, uint32 _blockTimestampLast)
    {
        _reserve0 = reserve0;
        _reserve1 = reserve1;
        _blockTimestampLast = blockTimestampLast;
    }

    function _safeTransfer(address token, address to, uint256 value) private {
        (bool success, bytes memory data) = token.call(
            abi.encodeWithSelector(IDeFiveToken.transfer.selector, to, value)
        );
        require(success && (data.length == 0 || abi.decode(data, (bool))), "DeFive: TRANSFER_FAILED");
    }

    function _update(uint256 balance0, uint256 balance1, uint112 _reserve0, uint112 _reserve1) private {
        require(balance0 <= type(uint112).max && balance1 <= type(uint112).max, "DeFive: OVERFLOW");
        uint32 blockTimestamp = uint32(block.timestamp % 2 ** 32);
        unchecked {
            uint32 timeElapsed = blockTimestamp - blockTimestampLast;
            if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {
                price0CumulativeLast += uint256(UQ112x112.encode(_reserve1).uqdiv(_reserve0)) * timeElapsed;
                price1CumulativeLast += uint256(UQ112x112.encode(_reserve0).uqdiv(_reserve1)) * timeElapsed;
            }
        }
        reserve0 = uint112(balance0);
        reserve1 = uint112(balance1);
        blockTimestampLast = blockTimestamp;
        emit Sync(reserve0, reserve1);
    }

    function _mintFee(uint112 _reserve0, uint112 _reserve1) private {
        uint256 _kLast = kLast;
        if (_kLast != 0) {
            uint256 rootK = Math.sqrt(uint256(_reserve0) * _reserve1);
            uint256 rootKLast = Math.sqrt(_kLast);
            if (rootK > rootKLast) {
                uint256 liquidity = (totalSupply * (rootK - rootKLast)) / (rootK * 3 + rootKLast);

                if (liquidity > 0) {
                    // Cache factory and fee recipient addresses
                    address _factory = factory;
                    address feeToDevs = IDeFiveFactory(_factory).feeToDevs();
                    address feeToGbm = IDeFiveFactory(_factory).feeToGbm();

                    // Mint half liquidity to each fee recipient
                    uint256 halfLiquidity = liquidity / 2;
                    _mint(feeToDevs, halfLiquidity);
                    _mint(feeToGbm, halfLiquidity);
                }
            }
        }
    }

    function mint(address to) external override lock returns (uint256 liquidity) {
        (uint112 _reserve0, uint112 _reserve1, ) = getReserves();
        uint256 balance0 = IDeFiveToken(token0).balanceOf(address(this));
        uint256 balance1 = IDeFiveToken(token1).balanceOf(address(this));
        uint256 amount0 = balance0 - _reserve0;
        uint256 amount1 = balance1 - _reserve1;

        _mintFee(_reserve0, _reserve1);
        uint256 _totalSupply = totalSupply;
        if (_totalSupply == 0) {
            liquidity = Math.sqrt(amount0 * amount1) - MINIMUM_LIQUIDITY;
            _mint(address(0), MINIMUM_LIQUIDITY);
        } else {
            liquidity = Math.min((amount0 * _totalSupply) / _reserve0, (amount1 * _totalSupply) / _reserve1);
        }
        require(liquidity > 0, "DeFive: INSUFFICIENT_LIQUIDITY_MINTED");
        _mint(to, liquidity);

        _update(balance0, balance1, _reserve0, _reserve1);
        kLast = uint256(reserve0) * reserve1;
        emit Mint(msg.sender, amount0, amount1);
    }

    function burn(address to) external override lock returns (uint256 amount0, uint256 amount1) {
        (uint112 _reserve0, uint112 _reserve1, ) = getReserves();
        address _token0 = token0;
        address _token1 = token1;
        uint256 balance0 = IDeFiveToken(_token0).balanceOf(address(this));
        uint256 balance1 = IDeFiveToken(_token1).balanceOf(address(this));
        uint256 liquidity = balanceOf[address(this)];

        _mintFee(_reserve0, _reserve1);
        uint256 _totalSupply = totalSupply;
        amount0 = (liquidity * balance0) / _totalSupply;
        amount1 = (liquidity * balance1) / _totalSupply;
        require(amount0 > 0 && amount1 > 0, "DeFive: INSUFFICIENT_LIQUIDITY_BURNED");
        _burn(address(this), liquidity);
        _safeTransfer(_token0, to, amount0);
        _safeTransfer(_token1, to, amount1);
        balance0 = IDeFiveToken(_token0).balanceOf(address(this));
        balance1 = IDeFiveToken(_token1).balanceOf(address(this));

        _update(balance0, balance1, _reserve0, _reserve1);
        kLast = uint256(reserve0) * reserve1;
        emit Burn(msg.sender, amount0, amount1, to);
    }

    function swap(uint256 amount0Out, uint256 amount1Out, address to, bytes calldata data) external override lock {
        require(amount0Out > 0 || amount1Out > 0, "DeFive: INSUFFICIENT_OUTPUT_AMOUNT");
        (uint112 _reserve0, uint112 _reserve1, ) = getReserves();
        require(amount0Out < _reserve0 && amount1Out < _reserve1, "DeFive: INSUFFICIENT_LIQUIDITY");
        uint256 balance0;
        uint256 balance1;

        {
            address _token0 = token0;
            address _token1 = token1;
            require(to != _token0 && to != _token1, "DeFive: INVALID_TO");
            if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out);
            if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out);

            if (data.length > 0) IDeFiveCallee(to).deFiveCall(msg.sender, amount0Out, amount1Out, data);

            balance0 = IDeFiveToken(_token0).balanceOf(address(this));
            balance1 = IDeFiveToken(_token1).balanceOf(address(this));
        }

        uint256 amount0In = balance0 > _reserve0 - amount0Out ? balance0 - (_reserve0 - amount0Out) : 0;
        uint256 amount1In = balance1 > _reserve1 - amount1Out ? balance1 - (_reserve1 - amount1Out) : 0;
        require(amount0In > 0 || amount1In > 0, "DeFive: INSUFFICIENT_INPUT_AMOUNT");
        {
            uint256 balance0Adjusted = balance0 * 10000 - amount0In * 18;
            uint256 balance1Adjusted = balance1 * 10000 - amount1In * 18;
            require(balance0Adjusted * balance1Adjusted >= uint256(_reserve0) * _reserve1 * (10000 ** 2), "DeFive: K");
        }

        _update(balance0, balance1, _reserve0, _reserve1);
        emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
    }

    function skim(address to) external override lock {
        address _token0 = token0;
        address _token1 = token1;
        _safeTransfer(_token0, to, IDeFiveToken(_token0).balanceOf(address(this)) - reserve0);
        _safeTransfer(_token1, to, IDeFiveToken(_token1).balanceOf(address(this)) - reserve1);
    }

    function sync() external override lock {
        _update(
            IDeFiveToken(token0).balanceOf(address(this)),
            IDeFiveToken(token1).balanceOf(address(this)),
            reserve0,
            reserve1
        );
    }
}

// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

interface IDeFiveCallee {
    function deFiveCall(address sender, uint256 amount0, uint256 amount1, bytes calldata data) external;
}

// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

interface IDeFiveFactory {
    event PairCreated(address indexed token0, address indexed token1, address pair, uint256);

    event SetFeeToDevs(address indexed sender, address indexed feeToDevs);

    event SetFeeToGbm(address indexed sender, address indexed feeToGbm);

    event SetFeeToDevsSetter(address indexed sender, address indexed feeToDevsSetter);

    event SetFeeToGbmSetter(address indexed sender, address indexed feeToGbmSetter);

    function feeToDevs() external view returns (address);

    function feeToGbm() external view returns (address);

    function feeToDevsSetter() external view returns (address);

    function feeToGbmSetter() external view returns (address);

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

    function allPairs(uint256) external view returns (address pair);

    function allPairsLength() external view returns (uint256);

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

    function setFeeToDevs(address _feeToDevs) external;

    function setFeeToGbm(address _feeToGbm) external;

    function setFeeToDevsSetter(address _feeToDevsSetter) external;

    function setFeeToGbmSetter(address _feeToGbmSetter) external;
}

// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

import { IDeFiveToken } from "./IDeFiveToken.sol";

interface IDeFivePair is IDeFiveToken {
    event Mint(address indexed sender, uint256 amount0, uint256 amount1);

    event Burn(address indexed sender, uint256 amount0, uint256 amount1, address indexed to);

    event Swap(
        address indexed sender,
        uint256 amount0In,
        uint256 amount1In,
        uint256 amount0Out,
        uint256 amount1Out,
        address indexed to
    );

    event Sync(uint112 reserve0, uint112 reserve1);

    function MINIMUM_LIQUIDITY() external pure returns (uint256);

    function factory() external view returns (address);

    function token0() external view returns (address);

    function token1() external view returns (address);

    function getReserves() external view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);

    function price0CumulativeLast() external view returns (uint256);

    function price1CumulativeLast() external view returns (uint256);

    function kLast() external view returns (uint256);

    function mint(address to) external returns (uint256 liquidity);

    function burn(address to) external returns (uint256 amount0, uint256 amount1);

    function swap(uint256 amount0Out, uint256 amount1Out, address to, bytes calldata data) external;

    function skim(address to) external;

    function sync() external;

    function initialize(address, address) external;
}

// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

interface IDeFiveToken {
    event Approval(address indexed owner, address indexed spender, uint256 value);

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

    function name() external pure returns (string memory);

    function symbol() external pure returns (string memory);

    function decimals() external pure returns (uint8);

    function totalSupply() external view returns (uint256);

    function balanceOf(address owner) external view returns (uint256);

    function allowance(address owner, address spender) external view returns (uint256);

    function approve(address spender, uint256 value) external returns (bool);

    function transfer(address to, uint256 value) external returns (bool);

    function transferFrom(address from, address to, uint256 value) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);

    function PERMIT_TYPEHASH() external pure returns (bytes32);

    function nonces(address owner) external view returns (uint256);

    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;
}

// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

// a library for performing various math operations

library Math {
    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;
        }
    }
}

// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

// a library for handling binary fixed point numbers (https://en.wikipedia.org/wiki/Q_(number_format))

// range: [0, 2**112 - 1]
// resolution: 1 / 2**112

library UQ112x112 {
    uint224 constant Q112 = 2 ** 112;

    // encode a uint112 as a UQ112x112
    function encode(uint112 y) internal pure returns (uint224 z) {
        z = uint224(y) * Q112; // never overflows
    }

    // divide a UQ112x112 by a uint112, returning a UQ112x112
    function uqdiv(uint224 x, uint112 y) internal pure returns (uint224 z) {
        z = x / uint224(y);
    }
}