区块链是一个去中心化的分布式数据库，该数据库由一串使用密码学方法产生的数据区块有序连接而成，区块中包含有一定时间内产生的无法被篡改的数据记录信息。
区块链技术是利用块链式数据结构来验证与存储数据、利用分布式节点共识算法来生成和更新数据、利用密码学的方式保证数据传输和访问的安全、利用由自动化脚本代码组成的智能合约来编程和操作数据的一种全新的分布式基础架构与计算范式。
区块链技术模型自下而上包括数据层、网络层、共识层、激励层、合约层和应用层。每一层分别具备一项核心功能，不同层级之间相互配合，共同构建一个去中心的价值传输体系。
pragma solidity=0.5.16;
import'./interfaces/IUniswapV2Pair.sol';
import'./UniswapV2ERC20.sol';
import'./libraries/Math.sol';
import'./libraries/UQ112x112.sol';
import'./interfaces/IERC20.sol';
import'./interfaces/IUniswapV2Factory.sol';
import'./interfaces/IUniswapV2Callee.sol';
contract UniswapV2Pair is IUniswapV2Pair,UniswapV2ERC20{
using SafeMath for uint;
using UQ112x112 for uint224;
uint public constant MINIMUM_LIQUIDITY=10**3;
bytes4 private constant SELECTOR=bytes4(keccak256(bytes('transfer(address,uint256)')));
address public factory;
address public token0;
address public token1;
uint112 private reserve0;//uses single storage slot,accessible via getReserves
uint112 private reserve1;//uses single storage slot,accessible via getReserves
uint32 private blockTimestampLast;//uses single storage slot,accessible via getReserves
uint public price0CumulativeLast;
uint public price1CumulativeLast;
uint public kLast;//reserve0*reserve1,as of immediately after the most recent liquidity event
uint private unlocked=1;
modifier lock(){
require(unlocked==1,'UniswapV2:LOCKED');
unlocked=0;
_;
unlocked=1;
}
function getReserves()public view returns(uint112 _reserve0,uint112 _reserve1,uint32 _blockTimestampLast){
_reserve0=reserve0;
_reserve1=reserve1;
_blockTimestampLast=blockTimestampLast;
}
function _safeTransfer(address token,address to,uint value)private{
(bool success,bytes memory data)=token.call(abi.encodeWithSelector(SELECTOR,to,value));
require(success&&(data.length==0||abi.decode(data,(bool))),'UniswapV2:TRANSFER_FAILED');
}
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(uint112 reserve0,uint112 reserve1);
constructor()public{
factory=msg.sender;
}
//called once by the factory at time of deployment
function initialize(address _token0,address _token1)external{
require(msg.sender==factory,'UniswapV2:FORBIDDEN');//sufficient check
token0=_token0;
token1=_token1;
}
//update reserves and,on the first call per block,price accumulators
function _update(uint balance0,uint balance1,uint112 _reserve0,uint112 _reserve1)private{
require(balance0<=uint112(-1)&&balance1<=uint112(-1),'UniswapV2:OVERFLOW');
uint32 blockTimestamp=uint32(block.timestamp%2**32);
uint32 timeElapsed=blockTimestamp-blockTimestampLast;//overflow is desired
if(timeElapsed>0&&_reserve0!=0&&_reserve1!=0){
//*never overflows,and+overflow is desired
price0CumulativeLast+=uint(UQ112x112.encode(_reserve1).uqdiv(_reserve0))*timeElapsed;
price1CumulativeLast+=uint(UQ112x112.encode(_reserve0).uqdiv(_reserve1))*timeElapsed;
}
reserve0=uint112(balance0);
reserve1=uint112(balance1);
blockTimestampLast=blockTimestamp;
emit Sync(reserve0,reserve1);
}
//if fee is on,mint liquidity equivalent to 1/6th of the growth in sqrt(k)
function _mintFee(uint112 _reserve0,uint112 _reserve1)private returns(bool feeOn){
address feeTo=IUniswapV2Factory(factory).feeTo();
feeOn=feeTo!=address(0);
uint _kLast=kLast;//gas savings
if(feeOn){
if(_kLast!=0){
uint rootK=Math.sqrt(uint(_reserve0).mul(_reserve1));
uint rootKLast=Math.sqrt(_kLast);
if(rootK>rootKLast){
uint numerator=totalSupply.mul(rootK.sub(rootKLast));
uint denominator=rootK.mul(5).add(rootKLast);
uint liquidity=numerator/denominator;
if(liquidity>0)_mint(feeTo,liquidity);
}
}
}else if(_kLast!=0){
kLast=0;
}
}
//this low-level function should be called from a contract which performs important safety checks
function mint(address to)external lock returns(uint liquidity){
(uint112 _reserve0,uint112 _reserve1,)=getReserves();//gas savings
uint balance0=IERC20(token0).balanceOf(address(this));
uint balance1=IERC20(token1).balanceOf(address(this));
uint amount0=balance0.sub(_reserve0);
uint amount1=balance1.sub(_reserve1);
bool feeOn=_mintFee(_reserve0,_reserve1);
uint _totalSupply=totalSupply;//gas savings,must be defined here since totalSupply can update in _mintFee
if(_totalSupply==0){
liquidity=Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);
_mint(address(0),MINIMUM_LIQUIDITY);//permanently lock the first MINIMUM_LIQUIDITY tokens
}else{
liquidity=Math.min(amount0.mul(_totalSupply)/_reserve0,amount1.mul(_totalSupply)/_reserve1);
}
require(liquidity>0,'UniswapV2:INSUFFICIENT_LIQUIDITY_MINTED');
_mint(to,liquidity);
_update(balance0,balance1,_reserve0,_reserve1);
if(feeOn)kLast=uint(reserve0).mul(reserve1);//reserve0 and reserve1 are up-to-date
emit Mint(msg.sender,amount0,amount1);
}
//this low-level function should be called from a contract which performs important safety checks
function burn(address to)external lock returns(uint amount0,uint amount1){
(uint112 _reserve0,uint112 _reserve1,)=getReserves();//gas savings
address _token0=token0;//gas savings
address _token1=token1;//gas savings
uint balance0=IERC20(_token0).balanceOf(address(this));
uint balance1=IERC20(_token1).balanceOf(address(this));
uint liquidity=balanceOf[address(this)];
bool feeOn=_mintFee(_reserve0,_reserve1);
uint _totalSupply=totalSupply;//gas savings,must be defined here since totalSupply can update in _mintFee
amount0=liquidity.mul(balance0)/_totalSupply;//using balances ensures pro-rata distribution
amount1=liquidity.mul(balance1)/_totalSupply;//using balances ensures pro-rata distribution
require(amount0>0&&amount1>0,'UniswapV2:INSUFFICIENT_LIQUIDITY_BURNED');
_burn(address(this),liquidity);
_safeTransfer(_token0,to,amount0);
_safeTransfer(_token1,to,amount1);
balance0=IERC20(_token0).balanceOf(address(this));
balance1=IERC20(_token1).balanceOf(address(this));
_update(balance0,balance1,_reserve0,_reserve1);
if(feeOn)kLast=uint(reserve0).mul(reserve1);//reserve0 and reserve1 are up-to-date
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(amount0Out>0||amount1Out>0,'UniswapV2:INSUFFICIENT_OUTPUT_AMOUNT');
(uint112 _reserve0,uint112 _reserve1,)=getReserves();//gas savings
require(amount0Out<_reserve0&&amount1Out<_reserve1,'UniswapV2:INSUFFICIENT_LIQUIDITY');
uint balance0;
uint balance1;
{//scope for _token{0,1},avoids stack too deep errors
address _token0=token0;
address _token1=token1;
require(to!=_token0&&to!=_token1,'UniswapV2: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)IUniswapV2Callee(to).uniswapV2Call(msg.sender,amount0Out,amount1Out,data);
balance0=IERC20(_token0).balanceOf(address(this));
balance1=IERC20(_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,'UniswapV2:INSUFFICIENT_INPUT_AMOUNT');
{//scope for reserve{0,1}Adjusted,avoids stack too deep errors
uint balance0Adjusted=balance0.mul(1000).sub(amount0In.mul(3));
uint balance1Adjusted=balance1.mul(1000).sub(amount1In.mul(3));
require(balance0Adjusted.mul(balance1Adjusted)>=uint(_reserve0).mul(_reserve1).mul(1000**2),'UniswapV2: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=token0;//gas savings
address _token1=token1;//gas savings
_safeTransfer(_token0,to,IERC20(_token0).balanceOf(address(this)).sub(reserve0));
_safeTransfer(_token1,to,IERC20(_token1).balanceOf(address(this)).sub(reserve1));
}
//force reserves to match balances
function sync()external lock{
_update(IERC20(token0).balanceOf(address(this)),IERC20(token1).balanceOf(address(this)),reserve0,reserve1);
}
}
