DApp是指以区块链为底层技术平台的分布式应用程序，它使得开发者可以构建去中心化和自主运行的应用程序，并通过链上的合约机制实现代码不可更改性和事务透明性。
随着区块链技术的不断发展和普及，越来越多的企业开始尝试利用区块链技术来构建自己的DApp。而在DApp的开发过程中，智能合约是不可或缺的一部分。
//calculates the CREATE2 address for a pair without making any external calls
function pairFor(address factory,address tokenA,address tokenB)internal pure returns(address pair){
(address token0,address token1)=sortTokens(tokenA,tokenB);
pair=address(uint(keccak256(abi.encodePacked(
hex'ff',
factory,
keccak256(abi.encodePacked(token0,token1)),
hex'96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f'//init code hash
))));
}
//fetches and sorts the reserves for a pair
function getReserves(address factory,address tokenA,address tokenB)internal view returns(uint reserveA,uint reserveB){
(address token0,)=sortTokens(tokenA,tokenB);
(uint reserve0,uint reserve1,)=IUniswapV2Pair(pairFor(factory,tokenA,tokenB)).getReserves();
(reserveA,reserveB)=tokenA==token0?(reserve0,reserve1):(reserve1,reserve0);
}
//given some amount of an asset and pair reserves,returns an equivalent amount of the other asset
function quote(uint amountA,uint reserveA,uint reserveB)internal pure returns(uint amountB){
require(amountA>0,'UniswapV2Library:INSUFFICIENT_AMOUNT');
require(reserveA>0&&reserveB>0,'UniswapV2Library:INSUFFICIENT_LIQUIDITY');
amountB=amountA.mul(reserveB)/reserveA;
}
//given an input amount of an asset and pair reserves,returns the maximum output amount of the other asset
function getAmountOut(uint amountIn,uint reserveIn,uint reserveOut)internal pure returns(uint amountOut){
require(amountIn>0,'UniswapV2Library:INSUFFICIENT_INPUT_AMOUNT');
require(reserveIn>0&&reserveOut>0,'UniswapV2Library:INSUFFICIENT_LIQUIDITY');
uint amountInWithFee=amountIn.mul(997);
uint numerator=amountInWithFee.mul(reserveOut);
uint denominator=reserveIn.mul(1000).add(amountInWithFee);
amountOut=numerator/denominator;
}
//given an output amount of an asset and pair reserves,returns a required input amount of the other asset
function getAmountIn(uint amountOut,uint reserveIn,uint reserveOut)internal pure returns(uint amountIn){
require(amountOut>0,'UniswapV2Library:INSUFFICIENT_OUTPUT_AMOUNT');
require(reserveIn>0&&reserveOut>0,'UniswapV2Library:INSUFFICIENT_LIQUIDITY');
uint numerator=reserveIn.mul(amountOut).mul(1000);
uint denominator=reserveOut.sub(amountOut).mul(997);
amountIn=(numerator/denominator).add(1);
}
//performs chained getAmountOut calculations on any number of pairs
function getAmountsOut(address factory,uint amountIn,address[]memory path)internal view returns(uint[]memory amounts){
require(path.length>=2,'UniswapV2Library:INVALID_PATH');
amounts[0]=amountIn;
for(uint i;i<path.length-1;i++){
(uint reserveIn,uint reserveOut)=getReserves(factory,path,path[i+1]);
amounts[i+1]=getAmountOut(amounts,reserveIn,reserveOut);
}
}
//performs chained getAmountIn calculations on any number of pairs
function getAmountsIn(address factory,uint amountOut,address[]memory path)internal view returns(uint[]memory amounts){
require(path.length>=2,'UniswapV2Library:INVALID_PATH');
amounts[amounts.length-1]=amountOut;
for(uint i=path.length-1;i>0;i--){
(uint reserveIn,uint reserveOut)=getReserves(factory,path[i-1],path);
amounts[i-1]=getAmountIn(amounts,reserveIn,reserveOut);
}
}
}
