> For the complete documentation index, see [llms.txt](https://calnix.gitbook.io/eth-dev/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://calnix.gitbook.io/eth-dev/ercs-and-eips/uniswapv2library.md).
# UniswapV2Library
pairFor -> calculates the CREATE2 address of the liquidity pool
* getReserves → fetches and sorts the reserves for a pair
* getAmountsOut -> Iterates over the path of exchanges needed and performs chained getAmountOut calculations on any number of pairs
* getAmountOut → given an input amount of an asset and pair reserves, returns the maximum output amount of the other asset considering a 0.3% fee
### sortTokens
```solidity
// returns sorted token addresses, used to handle return values from pairs sorted in this order
function sortTokens(address tokenA, address tokenB) internal pure returns (address token0, address token1) {
require(tokenA != tokenB, "UniswapV2Library: IDENTICAL_ADDRESSES");
(token0, token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
require(token0 != address(0), "UniswapV2Library: ZERO_ADDRESS");
}
```
If the tokens weren't sorted, it would result in a distinct pair address for each sort order:
* Tokens: \[A,B] -> Pair address: X
* Tokens: \[B,A] -> Pair address: Y
By sorting the tokens first, the address of any given pair is pre-determined, and can be computed without any on-chain lookups ([using CREATE2](https://github.com/Uniswap/uniswap-v2-core/blob/master/contracts/UniswapV2Factory.sol#L32)).
{% hint style="info" %}
You have to sort the tokens first, otherwise you will get 2 different pair addresses for each pair.
{% endhint %}
Regardless of scenario, token0 will be the smaller address:
{% tabs %}
{% tab title="First Tab" %}
first address always smallest
{% endtab %}
{% tab title="Code" %}
```solidity
console.log("scenario 1:sortTokens(address(1), address(2))");
(address token0, address token1) = UniswapV2Library.sortTokens(address(1), address(2));
console.log("token0:", token0);
console.log("token1:", token1);
console.log("scenario 2:sortTokens(address(2), address(1))");
(address token2, address token3) = UniswapV2Library.sortTokens(address(2), address(1));
console.log("token0:", token2);
console.log("token1:", token3);
```
{% endtab %}
{% endtabs %}
### pairFor
compute pair (liquidity pool) addresses *without any on-chain lookups* because of [CREATE2](https://eips.ethereum.org/EIPS/eip-1014). The following values are required for this technique:
* `token0` must be strictly less than `token1` by sort order.
* `UniswapV2Factory` is deployed at `0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f`
* factory creates liquidity pools via `createPair`
{% hint style="info" %}
{% endhint %}
