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pragma solidity =0.6.6;
import '@uniswap/v2-core/contracts/interfaces/IUniswapV2Factory.sol';
import '@uniswap/v2-core/contracts/interfaces/IUniswapV2Pair.sol';
import '@uniswap/lib/contracts/libraries/FixedPoint.sol';
import '../libraries/UniswapV2OracleLibrary.sol';
import '../libraries/UniswapV2Library.sol';
// fixed window oracle that recomputes the average price for the entire period once every period
// note that the price average is only guaranteed to be over at least 1 period, but may be over a longer period
contract ExampleOracleSimple {
using FixedPoint for *;
uint public constant PERIOD = 24 hours;
IUniswapV2Pair immutable pair;
address public immutable token0;
address public immutable token1;
uint public price0CumulativeLast;
uint public price1CumulativeLast;
uint32 public blockTimestampLast;
FixedPoint.uq112x112 public price0Average;
FixedPoint.uq112x112 public price1Average;
constructor(address factory, address tokenA, address tokenB) public {
IUniswapV2Pair _pair = IUniswapV2Pair(UniswapV2Library.pairFor(factory, tokenA, tokenB));
pair = _pair;
token0 = _pair.token0();
token1 = _pair.token1();
price0CumulativeLast = _pair.price0CumulativeLast(); // fetch the current accumulated price value (1 / 0)
price1CumulativeLast = _pair.price1CumulativeLast(); // fetch the current accumulated price value (0 / 1)
uint112 reserve0;
uint112 reserve1;
(reserve0, reserve1, blockTimestampLast) = _pair.getReserves();
require(reserve0 != 0 && reserve1 != 0, 'ExampleOracleSimple: NO_RESERVES'); // ensure that there's liquidity in the pair
}
function update() external {
(uint price0Cumulative, uint price1Cumulative, uint32 blockTimestamp) =
UniswapV2OracleLibrary.currentCumulativePrices(address(pair));
uint32 timeElapsed = blockTimestamp - blockTimestampLast; // overflow is desired
// ensure that at least one full period has passed since the last update
require(timeElapsed >= PERIOD, 'ExampleOracleSimple: PERIOD_NOT_ELAPSED');
// overflow is desired, casting never truncates
// cumulative price is in (uq112x112 price * seconds) units so we simply wrap it after division by time elapsed
price0Average = FixedPoint.uq112x112(uint224((price0Cumulative - price0CumulativeLast) / timeElapsed));
price1Average = FixedPoint.uq112x112(uint224((price1Cumulative - price1CumulativeLast) / timeElapsed));
price0CumulativeLast = price0Cumulative;
price1CumulativeLast = price1Cumulative;
blockTimestampLast = blockTimestamp;
}
// note this will always return 0 before update has been called successfully for the first time.
function consult(address token, uint amountIn) external view returns (uint amountOut) {
if (token == token0) {
amountOut = price0Average.mul(amountIn).decode144();
} else {
require(token == token1, 'ExampleOracleSimple: INVALID_TOKEN');
amountOut = price1Average.mul(amountIn).decode144();
}
}
}