0.8 compatibility, uniswap v3 oracle

gistfile1.txt

    function _checkSlippage(uint160 _swapThresholdPrice, bool zeroForOne)
        private
        view
    {
        uint32[] memory secondsAgo = new uint32[](2);
        secondsAgo[0] = _observationSeconds;
        secondsAgo[1] = 0;

        (int56[] memory tickCumulatives, ) = pool.observe(secondsAgo);

        require(tickCumulatives.length == 2, "array length");
        uint160 avgSqrtRatioX96;
        unchecked {
            int24 avgTick =
                int24(
                    (tickCumulatives[1] - tickCumulatives[0]) /
                        int56(uint56(_observationSeconds))
                );
            avgSqrtRatioX96 = avgTick.getSqrtRatioAtTick();
        }

        uint160 maxSlippage = (avgSqrtRatioX96 * _maxSlippageBPS) / 10000;
        if (zeroForOne) {
            require(
                _swapThresholdPrice >= avgSqrtRatioX96 - maxSlippage,
                "unacceptable slippage"
            );
        } else {
            require(
                _swapThresholdPrice <= avgSqrtRatioX96 + maxSlippage,
                "unacceptable slippage"
            );
        }
    }