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UniswapV2OracleLibrary.sol
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UniswapV2OracleLibrary.sol
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pragma solidity >=0.5.0;
import '@uniswap/v2-core/contracts/interfaces/IUniswapV2Pair.sol';
import '@uniswap/lib/contracts/libraries/FixedPoint.sol';
// library with helper methods for oracles that are concerned with computing average prices
library UniswapV2OracleLibrary {
using FixedPoint for *;
// helper function that returns the current block timestamp within the range of uint32, i.e. [0, 2**32 - 1]
function currentBlockTimestamp() internal view returns (uint32) {
return uint32(block.timestamp % 2 ** 32);
}
// produces the cumulative price using counterfactuals to save gas and avoid a call to sync.
function currentCumulativePrices(
address pair
) internal view returns (uint price0Cumulative, uint price1Cumulative, uint32 blockTimestamp) {
blockTimestamp = currentBlockTimestamp();
price0Cumulative = IUniswapV2Pair(pair).price0CumulativeLast();
price1Cumulative = IUniswapV2Pair(pair).price1CumulativeLast();
// if time has elapsed since the last update on the pair, mock the accumulated price values
(uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast) = IUniswapV2Pair(pair).getReserves();
if (blockTimestampLast != blockTimestamp) {
// subtraction overflow is desired
uint32 timeElapsed = blockTimestamp - blockTimestampLast;
// addition overflow is desired
// counterfactual
price0Cumulative += uint(FixedPoint.fraction(reserve1, reserve0)._x) * timeElapsed;
// counterfactual
price1Cumulative += uint(FixedPoint.fraction(reserve0, reserve1)._x) * timeElapsed;
}
}
}