 = 2^( t / T1/2);
p_new = pLast * (1 - ) +  * p_old // p_old = current price_oracle
// eg. last price update / trade must have been executed within the past hour
uint256 lastPricesTimestamp = ICurveCryptoPool(CURVEPOOL).last_prices_timestamp();
require(block.timestamp - lastPricesTimestamp <= 1 hours, 'stale price');
uint256 lastPrice = ICurveCryptoPool(CURVEPOOL).last_prices();
uint256 oraclePrice = ICurveCryptoPool(CURVEPOOL).price_oracle();
uint256 percentDiff;
// eg. require difference in prices to be within 5%
if (lastPrice > oraclePrice) {
  percentDiff = (lastPrice - oraclePrice) * 1e18 / oraclePrice;
} else {
  percentDiff = (oraclePrice - lastPrice) * 1e18 / oraclePrice;
}
require(percentDiff <= 5e16, 'volatile market');
