1  pragma solidity >=0.5.0;
 2  
 3  import '@pangolindex/exchange-contracts/contracts/pangolin-core/interfaces/IPangolinPair.sol';
 4  import '@pangolindex/exchange-contracts/contracts/pangolin-lib/libraries/FixedPoint.sol';
 5  
 6  
 7  // library with helper methods for oracles that are concerned with computing average prices
 8  library PangolinOracleLibrary {
 9      using FixedPoint for *;
10  
11      // helper function that returns the current block timestamp within the range of uint32, i.e. [0, 2**32 - 1]
12      function currentBlockTimestamp() internal view returns (uint32) {
13          return uint32(block.timestamp % 2 ** 32);
14      }
15  
16      // produces the cumulative price using counterfactuals to save gas and avoid a call to sync.
17      function currentCumulativePrices(
18          address pair
19      ) internal view returns (uint price0Cumulative, uint price1Cumulative, uint32 blockTimestamp) {
20          blockTimestamp = currentBlockTimestamp();
21          price0Cumulative = IPangolinPair(pair).price0CumulativeLast();
22          price1Cumulative = IPangolinPair(pair).price1CumulativeLast();
23  
24          // if time has elapsed since the last update on the pair, mock the accumulated price values
25          (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast) = IPangolinPair(pair).getReserves();
26          if (blockTimestampLast != blockTimestamp) {
27              // subtraction overflow is desired
28              uint32 timeElapsed = blockTimestamp - blockTimestampLast;
29              // addition overflow is desired
30              // counterfactual
31              price0Cumulative += uint(FixedPoint.fraction(reserve1, reserve0)._x) * timeElapsed;
32              // counterfactual
33              price1Cumulative += uint(FixedPoint.fraction(reserve0, reserve1)._x) * timeElapsed;
34          }
35      }
36  }