DeFi Swap (Crypto.com)

1contract CroDefiSwapPair is ICroDefiSwapPair, CroDefiSwapERC20 {
2    using SafeMath  for uint;
3    using UQ112x112 for uint224;
4​
5    uint public constant MINIMUM_LIQUIDITY = 10**3;
6    bytes4 private constant SELECTOR = bytes4(keccak256(bytes('transfer(address,uint256)')));
7​
8    address public factory;
9    address public token0;
10    address public token1;
11​
12    uint112 private reserve0;           // uses single storage slot, accessible via getReserves
13    uint112 private reserve1;           // uses single storage slot, accessible via getReserves
14    uint32  private blockTimestampLast; // uses single storage slot, accessible via getReserves
15​
16    uint public price0CumulativeLast;
17    uint public price1CumulativeLast;
18    uint public kLast; // reserve0 * reserve1, as of immediately after the most recent liquidity event
19​
20    uint private unlocked = 1;
21    modifier lock() {
22        require(unlocked == 1, 'CroDefiSwap: LOCKED');
23        unlocked = 0;
24        _;
25        unlocked = 1;
26    }
27​
28    function getReserves() public view returns (uint112 _reserve0, uint112 _reserve1, uint32 _blockTimestampLast) {
29        _reserve0 = reserve0;
30        _reserve1 = reserve1;
31        _blockTimestampLast = blockTimestampLast;
32    }
33​
34    function _safeTransfer(address token, address to, uint value) private {
35        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(SELECTOR, to, value));
36        require(success && (data.length == 0 || abi.decode(data, (bool))), 'CroDefiSwap: TRANSFER_FAILED');
37    }
38​
39    event Mint(address indexed sender, uint amount0, uint amount1);
40    event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
41    event Swap(
42        address indexed sender,
43        uint amount0In,
44        uint amount1In,
45        uint amount0Out,
46        uint amount1Out,
47        address indexed to
48    );
49    event Sync(uint112 reserve0, uint112 reserve1);
50​
51    constructor() public {
52        factory = msg.sender;
53    }
54​
55    // called once by the factory at time of deployment
56    function initialize(address _token0, address _token1) external {
57        require(msg.sender == factory, 'CroDefiSwap: FORBIDDEN'); // sufficient check
58        token0 = _token0;
59        token1 = _token1;
60    }
61​
62    // update reserves and, on the first call per block, price accumulators
63    function _update(uint balance0, uint balance1, uint112 _reserve0, uint112 _reserve1) private {
64        require(balance0 <= uint112(-1) && balance1 <= uint112(-1), 'CroDefiSwap: OVERFLOW');
65        uint32 blockTimestamp = uint32(block.timestamp % 2**32);
66        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // overflow is desired
67        if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {
68            // * never overflows, and + overflow is desired
69            price0CumulativeLast += uint(UQ112x112.encode(_reserve1).uqdiv(_reserve0)) * timeElapsed;
70            price1CumulativeLast += uint(UQ112x112.encode(_reserve0).uqdiv(_reserve1)) * timeElapsed;
71        }
72        reserve0 = uint112(balance0);
73        reserve1 = uint112(balance1);
74        blockTimestampLast = blockTimestamp;
75        emit Sync(reserve0, reserve1);
76    }
77​
78    // if fee is on, mint liquidity equivalent to 1/6th of the growth in sqrt(k)
79    function _mintFee(uint112 _reserve0, uint112 _reserve1) private returns (bool feeOn) {
80        address feeTo = ICroDefiSwapFactory(factory).feeTo();
81        uint feeToBasisPoint = ICroDefiSwapFactory(factory).feeToBasisPoint();
82​
83        feeOn = (feeTo != address(0)) && (feeToBasisPoint > 0);
84        uint _kLast = kLast; // gas savings
85        if (feeOn) {
86            if (_kLast != 0) {
87                uint rootK = Math.sqrt(uint(_reserve0).mul(_reserve1));
88                uint rootKLast = Math.sqrt(_kLast);
89                if (rootK > rootKLast) {
90                    uint numerator = totalSupply.mul(rootK.sub(rootKLast));
91                    uint denominator = rootK.mul(feeToBasisPoint).add(rootKLast);
92                    uint liquidity = numerator / denominator;
93                    if (liquidity > 0) _mint(feeTo, liquidity);
94                }
95            }
96        } else if (_kLast != 0) {
97            kLast = 0;
98        }
99    }
100​
101    // this low-level function should be called from a contract which performs important safety checks
102    function mint(address to) external lock returns (uint liquidity) {
103        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
104        uint balance0 = IERC20(token0).balanceOf(address(this));
105        uint balance1 = IERC20(token1).balanceOf(address(this));
106        uint amount0 = balance0.sub(_reserve0);
107        uint amount1 = balance1.sub(_reserve1);
108​
109        bool feeOn = _mintFee(_reserve0, _reserve1);
110        uint _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
111        if (_totalSupply == 0) {
112            liquidity = Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);
113           _mint(address(0), MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
114        } else {
115            liquidity = Math.min(amount0.mul(_totalSupply) / _reserve0, amount1.mul(_totalSupply) / _reserve1);
116        }
117        require(liquidity > 0, 'CroDefiSwap: INSUFFICIENT_LIQUIDITY_MINTED');
118        _mint(to, liquidity);
119​
120        _update(balance0, balance1, _reserve0, _reserve1);
121        if (feeOn) kLast = uint(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
122        emit Mint(msg.sender, amount0, amount1);
123    }
124​
125    // this low-level function should be called from a contract which performs important safety checks
126    function burn(address to) external lock returns (uint amount0, uint amount1) {
127        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
128        address _token0 = token0;                                // gas savings
129        address _token1 = token1;                                // gas savings
130        uint balance0 = IERC20(_token0).balanceOf(address(this));
131        uint balance1 = IERC20(_token1).balanceOf(address(this));
132        uint liquidity = balanceOf[address(this)];
133​
134        bool feeOn = _mintFee(_reserve0, _reserve1);
135        uint _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
136        amount0 = liquidity.mul(balance0) / _totalSupply; // using balances ensures pro-rata distribution
137        amount1 = liquidity.mul(balance1) / _totalSupply; // using balances ensures pro-rata distribution
138        require(amount0 > 0 && amount1 > 0, 'CroDefiSwap: INSUFFICIENT_LIQUIDITY_BURNED');
139        _burn(address(this), liquidity);
140        _safeTransfer(_token0, to, amount0);
141        _safeTransfer(_token1, to, amount1);
142        balance0 = IERC20(_token0).balanceOf(address(this));
143        balance1 = IERC20(_token1).balanceOf(address(this));
144​
145        _update(balance0, balance1, _reserve0, _reserve1);
146        if (feeOn) kLast = uint(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
147        emit Burn(msg.sender, amount0, amount1, to);
148    }
149​
150    / this low-level function should be called from a contract which performs important safety checks
151    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external lock {
152        require(amount0Out > 0 || amount1Out > 0, 'CroDefiSwap: INSUFFICIENT_OUTPUT_AMOUNT');
153        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
154        require(amount0Out < _reserve0 && amount1Out < _reserve1, 'CroDefiSwap: INSUFFICIENT_LIQUIDITY');
155​
156        uint balance0;
157        uint balance1;
158        { / scope for _token{0,1}, avoids stack too deep errors
159        address _token0 = token0;
160        address _token1 = token1;
161        require(to != _token0 && to != _token1, 'CroDefiSwap: INVALID_TO');
162        if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
163        if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
164        if (data.length > 0) ICroDefiSwapCallee(to).croDefiSwapCall(msg.sender, amount0Out, amount1Out, data);
165        balance0 = IERC20(_token0).balanceOf(address(this));
166        balance1 = IERC20(_token1).balanceOf(address(this));
167        }
168        uint amount0In = balance0 > _reserve0 - amount0Out ? balance0 - (_reserve0 - amount0Out) : 0;
169        uint amount1In = balance1 > _reserve1 - amount1Out ? balance1 - (_reserve1 - amount1Out) : 0;
170        require(amount0In > 0 || amount1In > 0, 'CroDefiSwap: INSUFFICIENT_INPUT_AMOUNT');
171        { // scope for reserve{0,1}Adjusted, avoids stack too deep errors
172        uint magnifier = 10000;
173        uint totalFeeBasisPoint = ICroDefiSwapFactory(factory).totalFeeBasisPoint();
174        uint balance0Adjusted = balance0.mul(magnifier).sub(amount0In.mul(totalFeeBasisPoint));
175        uint balance1Adjusted = balance1.mul(magnifier).sub(amount1In.mul(totalFeeBasisPoint));
176        // reference: https://uniswap.org/docs/v2/protocol-overview/glossary/#constant-strapiuct-formula
177        require(balance0Adjusted.mul(balance1Adjusted) >= uint(_reserve0).mul(_reserve1).mul(magnifier**2), 'CroDefiSwap: Constant strapiuct formula condition not met!');
178        }
179​
180        _update(balance0, balance1, _reserve0, _reserve1);
181        emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
182    }
183​
184    // force balances to match reserves
185    function skim(address to) external lock {
186        address _token0 = token0; // gas savings
187        address _token1 = token1; // gas savings
188        _safeTransfer(_token0, to, IERC20(_token0).balanceOf(address(this)).sub(reserve0));
189        _safeTransfer(_token1, to, IERC20(_token1).balanceOf(address(this)).sub(reserve1));
190    }
191​
192    // force reserves to match balances
193    function sync() external lock {
194        _update(IERC20(token0).balanceOf(address(this)), IERC20(token1).balanceOf(address(this)), reserve0, reserve1);
195    }
196}

Solidity Contracts